Week definition on cowl tag

[396guy]

First post here so if this has been answered before I apologize and I'm not looking to decode a cowl tag but gather information on how the date is determined.  I'm in a Chevelle thread at Team Chevelle discussing body dates on trim/cowl tags vs. the date appearing on the build sheet and I assume the same would apply to the Camaro.  My questions concern the month/week date on a Fisher Body plate, a.k.a., trim or cowl tag  and the flow of the paperwork.  I know the date represents a month and week and have a specific question on how the 'week' is arrived at.

First, what physically constitutes a week of A, B, C, D, or E? 
1. I initially thought it was the physical week of a month.  If the 1st of the month started on a Wednesday, then Wednesday thru Saturday (1-4) were week A, 5-11, week B, etc.  But, some months would have 6 'weeks' using this method. 

2. My second thought is that week "A" are dates 1-7, week "B" are dates 8-14, up through week "E" dates of 29-31 where applicable regardless of the day of the week.  Using this second method, every month except Feb (except a leap year) would have weeks A..E.  It seems logical (therefore probably wrong) that the procedure for stamping the cowl tag would be simplified if a physical calendar was not required to convert a day's date into a week letter.  These had to be automated and stamped by the hundreds so what logic, program or human, determined when the date should change from 01A to 01B?  Whatever the logic involved this dating systems seems to hold true for the majority of cowl tag dates when compared to build sheet dates, but there are exceptions.  One example I know of, on a 1970 Chevelle, has a cowl tag date of 01A but a build sheet date of 01-09.

Second, reading the excellent "Assembly Process" page the cowl tag was installed on the Fisher Body side fairly early during the body framing stage.  The cowl tag obviously had not only the assembly date but other information that indicates (to me anyway) the car was locked into production even though a VIN hadn't been assigned yet by Chevrolet. 

Can I assume the initial paperwork to build the car would come from Chevrolet and note what colors, options, etc. are to be used and the date on the build sheet would be the date the car is initiated?  Assuming the body numbers and other groups of data from the build sheet are coded onto the cowl tag for tracking and when completed at Fisher and sent to Chevrolet for final assembly, the final sequence number (last 6 digits of the VIN) is then put on the build sheet; at least on Chevelles, this sequence number looks like it's stamped after the sheet was initially printed and in a different font and often at an angle in the upper right.

Question #2 is how does the date on the build sheet correlate to the body assembly date on the cowl tag?  Using the 01A/01-09 example above, how would a car who's conception date of January 9, 1970 get a body assembly date of the first week (01A) of January?  Assuming my theory of A=1-7, B=8-14, etc. I can see where a conception date of say 09-20 might get a "D" week (22-28) instead of a "C" week (15-21) coding if the car wasn't physically started for a day or two but not the other way around as in the case of the 01-09 car with an "A" week.

I guess the first thing to establish is how is the 'week' letter determined.  Second is the relationship between the build sheet date and the beginning of the car's build cycle.  Hopefully then the relationship between the two can be determined.  I'm looking forward to the discussion, thank you.

[KurtS]

It's been discussed here and on TC several times.

Summation:
There is no absolute relationship between the cowl tag and the calendar. The build date was for Fisher's use and they changed the date at their discretion....

[396guy]

Well, that's certainly disheartening news.  So when anyone like Team Chevelle, Team Camaro, CRG, Colvin's various 'by the numbers' books or any other decoding sites states that "A" is the first week, "B" is the second, etc. they're just parroting something that is essentially worthless information?

[67ss350camaro]

Well, that's certainly disheartening news.  So when anyone like Team Chevelle, Team Camaro, CRG, Colvin's various 'by the numbers' books or any other decoding sites states that "A" is the first week, "B" is the second, etc. they're just parroting something that is essentially worthless information?

Worthless?  All Kurt is saying is that you can't put specific dates to the letters.  It does tell you that a car built 11C was after a car built 11B.  You just don't know what dates.

[JohnZ]

Second, reading the excellent "Assembly Process" page the cowl tag was installed on the Fisher Body side fairly early during the body framing stage.  The cowl tag obviously had not only the assembly date but other information that indicates (to me anyway) the car was locked into production even though a VIN hadn't been assigned yet by Chevrolet. 

You also need to consider whether the car was built at a traditional Fisher Body/Chevrolet plant (where each plant was separate, and they were operated by two different GM Divisions), or whether the car was built at a GMAD (GM Assembly Division) plant. GMAD plants were operated by one Division, and their operations/processes were integrated based on what made sense for the assembly process, not by whether the parts and tooling were released by Fisher Body or by Chevrolet. GMAD plants had total control of the assembly process and production scheduling from the first welding fixture in the Body Shop to the roll-test machines, and had much more flexibility in how production was scheduled and tracked; they operated differently (and more efficiently) than the Fisher Body/Chevrolet plants.

[396guy]

Well, that's certainly disheartening news.  So when anyone like Team Chevelle, Team Camaro, CRG, Colvin's various 'by the numbers' books or any other decoding sites states that "A" is the first week, "B" is the second, etc. they're just parroting something that is essentially worthless information?

Worthless?  All Kurt is saying is that you can't put specific dates to the letters.  It does tell you that a car built 11C was after a car built 11B.  You just don't know what dates.

By worthless I simply mean that when some person or some site says a car was made the first week, "A" for example, it doesn't mean anything if you can't pin down what dates that first week consisted of, regardles of the month or the plant.  Apparently, a 'week' could be any number of days according to the whim of the plant and whether it's a Fisher Body/Chevrolet or GMAD plant makes no difference.  If that's the case, as it appears to be, then saying "A" is the first week is inconclusive to attempt to match the week letter to any specific dates when other data that are common to all plants, such as trim numbers, paint numbers, and body numbers on Chevelles at least up to 1968, are uniform in meaning.

I guess, to be accurate, every site or publication that says 01A is the first week in January should include a caveat that nobody knows what that means, as far as a date range the first week consists of, but it is known it's dated before 01B.  Not really the answer I was looking for but if that's the case, so be it. Kind of like saying one's birthday is in the Spring.  Don't know when but it's sometime after Winter and sometime before Summer. I appreciate your help. 

[Mark]

A week is a generally a week in the body code, you just can't say that the A week started on the 1st of the month, or the E (or D) week ended on the 30th of the month. 

Generally the A week of the month is the first FULL calendar week of a month.  For example if the month ended on a Tuesday, then that whole "assembly" week was part of the previous month even though there was only one calendar day in that month.  There are exceptions to that statement, and differences from one assembly plant to another so its not really worth worrying about.  Using the VIN numbers (at least for 69 and later cars) is a much better way of determining when in a month a particular car was built.

[KurtS]

I'm missing how it's worthless. It is approximate.
It's not specific to the day, but that's not what the date was used for by GM.

Sounds like it's worthless to you for more day-specific info. That's all.

[Flowjoe]

I'm missing how it's worthless. It is approximate.
It's not specific to the day, but that's not what the date was used for by GM.

Sounds like it's worthless to you for more day-specific info. That's all.

I realize that the VIN is a more accurate method by which to devine the "birthday" of one's car but isn't the build date on the trim tag  frequently used to determine date correctness of car components?   I often see questions on this board asking if  an engine/carb/rear axle/etc is correctly dated for the car...often the only evidence requested to make this determination is the build date and the date on the component in question.  Obvioulsy a gap of weeks in component date and build date (component date preceeding the build date of course) is a no brainer...but what about dates on components that are very, very close to the build date of the car?  (example:  a rear axle dated 10/1 - cast '69 - and a Norwood car with a build date of 10A - '69?  According to JohnZ in another discussion it took about 5-7 days for an axle to reach the Norwood plant...with a fudge factor in the build date as a dating device is such a scenario possible?  has it ever been observed?