This could be out of ignorance, that's why I'm posting it here.

But are there two "The Amazing Spider-Man"'s? One starts at '99 and has 40 comics, the other starts at '63 and has 315 appearances (and includes current arcs, CW etc).

Did I black out for a bit of Spidey history, or is there a dupe?

I think it ended and then was started again.

They tried re-numbering to cash in on a new #1 and so it'd be less intimidating for new readers seeing there were over 400 issues to catch up on. I think people complained. Marvel started having two sets of numbers, the new system and the old. Then with #500, they just went back to the old numbering system. I hate when they restart numbering. Let's preserve the history, man!