delco radios and speakers options

what year t/a's had the 2 speaker system? people on PY are telling me the 78 was the first year for the 2 speakers in the rear.
and 77 and older was only one in the rear.
what is correct? what years got a one speaker? of course they all had one in the front up to 79.


my build sheet reads

UN9 Radio Accommodation Package how more vague can this be.



UN9 was a pay-extra option called the "radio accommodation package". This came free with a radio, but was a pay-extra option if you didn't get a radio. From the abbreviation, UN9 on build sheets refers to the noise suppression capacitors on your alternator, fusebox, and blower motor.
For invoice purposes, UN9 included the windshield antenna [You must be registered and logged in to see this link.]. The antenna is always coded separately on build sheets. After 1979, you could also opt for a power antenna [You must be registered and logged in to see this link.] for extra money.
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here is the link to it. if any one need the same info
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all birds left GM with no radio but the car wired for it.

OR,
with a radio with a front and one back speaker. on the drivers side.

the 2nd speaker was a dealer install. ( if they did it at all)

1979 was the start of the 2 speakers in the rear. on all but firebirds. then it was up to the dealer to add the other , if they wanted.

Since 1970 Dual Rear Speakers were an option, usually included with a stereo radio. Option 411/U80 was available for all years of the second gen Firebird. See link below for Option list:

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