First I'll clear the Sonic CD versions for you:
- There is a 510 beta, which was up at SSRG. This beta is an obvious press release, since after 3 levels it will leave you a "Coming Soon" message.
- There is a 712 beta, built from the 510 one. It's almost finished, oly small differences are in it.
- Then comes the Japanese final: "Sonic CD final JPN 806"
- then the EU final, "Sonic CD final EU 827). Only difference between the JPN one is that its in 50 Hz.
- Then the US prerelease version, which is the 910 one. This one has the gameplay differences built for the US version (like you can reset one life by pressing a button while the game is paused), but the CD audio tracks are the same that's used for the JPN and EU versions. Most people call it 920 because the date of the files in the ISO is 20th September, but the header says 910, so I use 910.
- and finally the US final, "Sonic CD final US 1006". It has totally rewritten music on the CD tracks and in the videos. Ah yeah, and the files dates are 10 way off in this one too, its 1016 while the ISO header is 1006.
if you want to get them, check the SonikTeam FTP