Well I think I have 20+ schwinns now (40s / 50s / 60s). I think every one of them has the frame stamped a few months older than the hub (I would have to go back through all of them). The interesting thing is when you get into frames stamped at the end of the year but have the next years component / decal package (If I remember correct a traveler I have is stamped a end of year '62 but has early '63 parts). All the bikes I am talking about are originals. I don't think I have any schwinns that have the frame stamped the exact same month as the hub and not even one month apart, it is usually multiple months. GT has gone into this many times but from what I understand the frames were built and hung / set aside / put away whatever they did with them while they awaited production of the bike. Then some time later, the bike was built and all the parts were pulled to build the bike. From what I understand they didn't build a frame and then the guy immediately sent it to paint, wait on it to dry and then start building the bike. The assembly line / order fulfillment process would only work if frames were stacked / hung / shelved / whatever they did with them and ready to go so all components could be put on them. One thing I am not clear on is how custom orders were handled back then (pretty sure I have seen those order forms but don't recall exact parameters). Like if someone went into the store and didn't see the color scheme they wanted and then the order was put in and bare frame pulled, painted and built. Additionally, I don't understand the process of how many of each model and color went to each store. Like did the store owners fill out prospective order forms saying they need this many of this model with these paint schemes or what (so they had bikes on the floor ready for sale). From reading through some of the Schwinn Reporters it seemed like the stores address their clientele as needed and some specialized more in lightweights and some in heavyweights etc. I would assume it was up to each store to know their target audience and order the bikes they think they could sell and it wasn't managers at the Schwinn HQ figuring out how many bikes would go to each location, what models, and what color schemes. You guys tell me. BUT, I would have to go with GT and the frames from what I have seen are always older than the hubs.
Edit - I should also say that this understanding only works with the serial number dating where it gets precise to the day / month. Anything before that the serials are much more vague. So for instance if I date my frame serial to 11/07/1962 and the hub shows 63 - 1 then this is the logic I reference above.
Serials -
https://thecabe.com/forum/threads/schwinn-serial-number-reference.63993/#post-386403