This is a few weeks old but interesting and a lot of people around here like to do things right. So:
It’s much easier I think for the dealer to use the fender location but any location was up to the whim of the dealer. On a 2002 you had to use the A pillar and I’ve seen them on both sides.
That's it. Dealers could place aerials/antennas where they liked, on the E3 & E9. On the 02 there was the choice between A-pillar, centre of bootlid, and roof (mostly front or centre). On the 02 Cabriolet it was only centre of bootlid as the reinforced windshield frame served as rollbar. Never drill there.
Also the installation instructions were done by the radio manufacturers, not BMW so it likely varied that way also.
Wrong. BMW gives detailed instructions on how to retrofit a radio, an aerial, an electric aerial, or a rear speaker, with exact measurements: Repair Manual, section 65. Whether workshops or owners followed the instructions is a different story.
BMW only ever put the aerial on the left front wing on the E3. Karmann probably did the same with the E9, too little knowledge about the E9 to be sure.
Most Italian E3 have an electric aerial on the left rear wing. The importer never ordered works radios but retrofitted them in Italy, reasons see below. Exceptions are the 3.3 models.
It could be that some customers didn't want a radio. (Very few, I'm sure)
More than you'd guess, at least in Europe. Or they wanted one but not as expensive as BMW offered them. Lots of radios were retrofitted by the dealers prior to delivery, easy money for them and still a bargain for the customers.
I just thought that since totally for the US market, the radio etc would have been standard and not an option since the Bavaria was supposed to be an entry level luxury car.
Radio came as an option for the 3.0 S Bavaria, at least the early ones. It was standard (with 3 speakers) on the late 3.0 Si USA. Outside the US, only the 3.3 L & 3.3 Li came with a radio and always with the best there was. For some markets, importers may have ordered cars with radios only, that I don't know.
No external antenna was installed. I actually liked that because I ran a small amplified antenna under the front dash. Great reception, no outside holes for water.
I like that, too. If you rebuild a car today, this is probably the way to go.
This is what a veteran radio & TV technician told me: We always put the aerials on the rear wing, as far away from the ignition coil as possible. You could not trust the interference suppression kits, then. Only on Diesel cars we happily placed them on the front wing because the wiring was much shorter that way.