Maybe I'm crazy and going down a rabbit hole here. But looking at an SSC card, I started wondering what the different revisions are. I've seen people refer to them as revision A, B and C. Maybe other letters, but seems to usually be one of those 3. Most people seem to base that off the letter stamped at the end of the part number in the lower left. And, there seem to be at least two variations of the Apple part number - 670-0020 and 670-8020. Looking photos of these two part number cards, All the ICs appear to be laid out the same, discreet components all seem to be in the same spots. A very, very cursory review of visible traces seem to be the same. Both are silk screened almost 99% the same. Both carry the 1981 copyright and same component numbers. What differs seems to be the Apple logo and FCC ID are placed in different places. It's tough to see any real difference in the hardware.
Which makes me think there is no validity to basing a revision based off the stamped letter. The one thing I have seen, is two different ROM part numbers. The ROM is always either 341-0065-A or 341-0065-B. Although the B variant seems to be the one in most images. But in searching Apple ROM part numbers, only the A variant seems to come up in results for the SSC. Also, on Asimov there appears to be a dump of the A ROM, but not the B ROM. I really wonder what the difference is between them, if anything. It seems odd Apple would go through the trouble of changing part numbers on both the cards and ROMs if something didn't differ.