IIRC every RC disk had alpha binaries, only the RTM and later doesn't - because Alpha getting canned was declared in the short window between last RC and RTM, in a rather abrupt manner to everyone involved on the project.
Seems to indicate that the Release Candidate 3 builds for Alpha never made it out through official channels. I'm pretty sure beta and RC was one disc per flavor and architecture though: so x86 professional, x86 server, etc, and alpha pro/server/etc. A big bundle of discs would come from Redmond.
I know nt4 had all the archs on the release disc, but I don't think that was the plan for win2k
