When I was maybe 5 or 6, a teacher at school asked if anybody could name 3 roads. I proudly put my hand up and said "A1, M1 and A1(M)". The teacher said that no, they were all the same road. I felt so smug, and at such a young age, knowing that the teacher was clearly wrong and how stupid they must be if even I knew something like that and they didn't. And so began my first steps into nerdism...
Yeah, I think you're right. Where I lived, in Stevenage, the original A1 was renamed B197, although I wouldn't have known that at the time - only that while I'd been a passenger in the car, I'd seen both the A1 and A1(M) and signs to them fairly frequently.
I guess my teacher was right and my youthful smugness was unfounded and misplaced. :D
EDIT: I just googled a bit more and discovered that at least one map (the one inch map from 1963) labelled the old road as A1 and the new road as A1(M) as distinct roads on the same map. I doubt I'd have actually seen that though, as it was from well over a decade before I was born, although my dad had lived in Stevenage around that period so maybe he still referred to it by its old name and I'd just picked up on that. Or more likely, I was just wrong!