End of year transition serial to Juilian date correspondence guidelines?

Ok, so I picked up and odd ball here. The serial reads June 1980, headbadge date is November 10th, denoting 1981 model year. No biggie 99% of the time, except that it is an SX2000/Sting Cometition frame, 80 vs. 81 is the transition between the models and NOS decals are $100- I only want to purchase once because of the second oddity...


The headbadge is the correct baby blue and is likely original, the screws certainly show their age and blue is the correct badge color for a red bike, near as I can tell anyway as original red bikes are obscenely rare. Warranty replacement and maybe S.O. F/F kinda stuff only. But here's the catch- the bike was painted by the famous CycleArt in San Diego at some point in it's life. The dropouts show washer marks from the rear wheel having been installed once prior to paint, once after, so it wasn't (terribly) abused. But, and there's that word again, there is not a hint of typical brown Schwinn primer. The primer is grey, and even in the tiniest nooks and crannies of the BB and head tube there is no evidence of the blast-o-matic which would have applied the original primer. Even someone like CycleArt would not have bothered to clean the lat little bit of primer out a gas vent hole out of the center of the BB, and then not spray new primer in there (bare metal inside the BB and head tube currently). When held up to my original paint Radiant Red '79 Spitfire, the match is as exact as one could ever ask for, and this paint certainly shows it's age. I'd say 20 years+. With the bike came a pair of NOS or factory take-off DC 1020 brakes in blue, levers/cables/calipers, all datable parts dated 9/81 and have the look of maybe having been assembled at a bike shop but not installed on a bike, or if so only shortly for one. So perhaps someone got the frame from the corner of a shop in the past and the brakes were in the corner abandoned with it, and it passed through a bunch of hands together to me. Who knows? Maybe someone just put some parts of the same vintage together over the years planning to build the bike, no way to tell.

So, the operative question being, given that I have no provenance on the bike and can't attach it to a story, a racer, a shop or anyone who can say "Yeah, I remember, I ordered that special, got it raw, took it to them to paint because I could not order red" or a shop who only ran red bikes or whatever. Obviously I am going to contact CycleArt and pray they are OCD about record keeping, even from 30 years ago, and will have them spray a new coat of clear over the missing decals once I order them, but again the operative question- go by the serial and sticker it as an '80 SX2000 or the badge and sticker it as an '81 Sting Comp.

I suppose four months is not that long for a frame to sit around between welding and assembly, what kind of date spans do you guys see on your original bikes? is four months typical? Especially at end of year transitions? I only get to do this once since it will be under the clear and I don't want to end up shooting myself in the foot, but every original unpainted Schwinn frame I have ever seen was at least in primer...

What does the jury have to say on this?

Four months from when a serial number was recorded to the date stamped in a head badge is really not that uncommon. There were a couple years difference on a certain lightweights. From my research the build date from the serial number date varies and the shortest time I've seen between the two number dates was a month, or 30 days. The longest time span on bikes that I have owned was just over 3 months. The serial numbers were stamped on the bikes component, bottom bracket, rear dropout, head tube etc. and then that part was used to build a frame. There is a good chance that SN stamped part was not used to build a frame for days, weeks etc.. If that was my frame I would go with the build date on the headbadge to determine the model year. I've also noted that all the serial numbers stamped from mid Nov. and on were on the next years models.

Ossum opossum, that's about what I figured. Looking at the frame, it was clearly never a chrome frame as the boogers from the welds would have been polished out, and they are still there. So that makes it a painted frame from day one, and of frames I have seen that were released in primer for promotional customers those did not have headbadges. Not definitive by any means, but a breadcrumb anyway. Talked to CycleArt, and she said based on the Vista CA location in the decal, it was painted post 1990 or so, which luckily meant the records are computerized, but needless to say "red Schwinn" is not a very fortunate search string. Schwinn BMX, Sting etc. didn't give us any hits, so no go there. But that said, the color is dead on, so 99% someone walked in with a red frame and said 'match this', which combined with the boogers and the blue badge tells me there is a high likelihood this was an original red frame, and must have once been someone's baby, because why else would you spend so much money getting it redone in the correct red ($300 just to have the clear redone today) and must have known it was special not to just have it powdered a 'close enough' color for far less, but did it early enough before BMX values started going up... for everything except the Comp frames lol.

If you are worried about a couple of months difference I wouldn't. I have a 1977 Sprint lightweight with a frame date of 1975. I also have a 1975 Sprint with a frame date of 1974. Schwinn way over built these frames and because of dismal sales it took a long time to make them into bikes. Rogr