Ed, do you have any info that says they were dropped in 1969? Did they find they really did not serve any purpose after studies on '68 and earlier cars?
Warren, there are several threads on the NCRS regarding this and probably other sites as well, but the clincher is the AIM's.
For example (and see below), the 69 Camaro AIM shows the note John quoted and the 69 Corvette AIM doesn't have the reference to the collectors that the 68 AIM does. The only difference between the two is that the 69 Camaro AIM has the change note indicating that the change happened some time during the model year. No way to know exactly, but the date of 8-22-68 means it probably occurred either very early in production, or even before production started. The 69 Corvette AIM doesn't have a note, so that means it took place before production started. I've included pictures showing the 68 and 69 Camaro AIM differences and also the 68 and 69 Corvette differences below.
As for dealer installed radios, yes, it's very possible. There might even be a Service Note stating something to the fact that if customers complain of radio static noise to install the collectors, but as of yet I haven't found one.
Ed