Kurt, et all...
Here's what I've come up with from my few months of collecting data (and pictures) off of ebay. I've referenced cars that appear to be original. (Old, faded paint, Rusted, beat up, etc...) I've only included car that have been repainted (therefore quarters "may" have been replaced) if they DON'T have the vents. Also note the build date in parenthesis if known.
The following cars DO NOT have the vents:
124678N301906
124678L301547 (09B)
123678L301970 (09B)
124678N307736 (09B)
124678N312935 (09D)
124678N321915 (10A)
123678N322131
124678L322238
124678L326479 (01C)
123678N337204
124678N339825
124678N340521
124678N353526 (12A)
124678N368757 (01A)
Notice that every one of these are Convertibles, and even cars built in early January 1968 were still without vents!
The following "original appearing" cars DID have the vents:
124378N300809 (08D)
124378L314378
124378L318764 (12C)
As a matter of fact, I couldn’t find ANY Norwood Coupes WITHOUT the vents!!
The following early cars DO have the vents, but they've been repainted so they "may" have had quarters replaced. These are the earliest I have in the database with pictures of the vent area:
124378L300356 (08D)
124378N300945 (08D)
123378L315864
123378N307678
Not sure how helpful this info is, but it's a start.
Ed