Here is a thread I started a dozen years ago about my 1977 frame (embarrassed to admit it's still hanging up gathering dust).
https://www.bikeforums.net/classic-v...enovation.html
FWIW, it looks to me that this thread's subject frame has a serial number on the BB shell underside, where the serial (12470) on mine is, so that's a gauge, since BJ did at least use sequential numbering, though no "date code" I'm aware of. BITD BJ would look up in their book when your serial number was, and tell you that much. I don't know if the current owners (Woodrup) still have that info. I do have a set of "original" black letter with gold outlining BJ logotype decals for a frame of that vintage, some of the last the shop had (they'd moved on to the later slanted letter logo many years before) if OP is interested in a "recreation".
When having the frame repainted (locally), the rear brake bridge was replaced with a more modern version with a larger "knuckle" -- my instruction was to unbraze the (slightly crooked) existing one and re-fit/re-braze it, but my esteemed (not being sarcastic) bike surgeon decided to "improve" on it. Other than that, all I added was a set of water bottle braze-ons, since I don't like the bands on the old ones, and I do like chromed band-on brake housing and derailleur cable fittings.
I've attached a couple BJ catalog bits and bobs from 1976 and 1978 (one JPG, one PDF, different years). My frame, and I suspect OP's too, are the lower-end-but still quite satisfactory Gran Prix model, not the deluxe "Nuovo Olympus" (or Olympiad).
If you want to see a really swish BJ "Olympus" frame, do check out Stronglight's Flickr album here:
https://www.flickr.com/photos/strong...57606749255200
It has the same black-gold decals mentioned above, on orange.
