I just took possession of my sister's Superior that she bought new. She and I both bought one at the same time back in about 1976. Mine is long gone but hers has been sitting idle for 30 years at least. The serial number on the head tube is EM802860 which indicates May'76but the head badge is 2208 which is 1978. I know we didn't buy it in 78 because I bought my first car then and you know how that goes. Any info on their numbering systems back then that might explain the 2 year difference?

The 2208 number on the head badge is the date code of the 220th day of 1978, the production date. The EMxxxx number is when the frame was built. It seems Schwinn was using up previous stock of frames at the end of the Fillet Brazed Era.

Unless the headbadge was replaced the 2208 number indicates that the bike was built on Tuesday August 8th, 1978. Note that Schwinn stamped bare head tubes in batches before they were even brazed into the frames. I've seen head tube stamps on fillet brazed models that were up to 6 years earlier than the bikes were built suggesting that Schwinn kept pre-stamped head tubes in inventory and used them at random (i.e. not in numbered order) to build frames (and bikes) as necessary.

That's interesting, only the stamped head tubes. I assumed entire frames were pulled from existing old stock.

Have you ever seen a 78 model year bike with the kickstand/fender mount with an earlier head tube stamp?
Nothing to base it on except a couple bikes I've seen, but it appears the old stock was used up sometime in 1977.

She found the original receipt which says we bought them 5/14/79 and paid $225.75 for each. They must have had a few left from the prior year if it was made a year earlier.