Well, it's pretty easy. The 1.00 series were sort of "Work in progress" versions. The version numbering was 1.00A till 1.00Z. And as far as I know so far only 1.00G, 1.00H and 1.00O (?) have been found.

The versions that actually were officially released started from 1.20. And then of course there was a 1.21 and 1.23 patch. I think 1.22 was only on CD releases. 1.21, 1.22 and 1.23 are all compatible with eachother when it comes to online play.

I think someone accidentally put the wrong version on his abandonware site (abandonware is illegal in most cases, in case you don't know) and that's how it got spread across the internet.