What advantage do we get from separating 3 (downwards and upwards
compatible) from 4 (small fixes)? Under what conditions would one ever
want to accept a version that (supposedly) differs only by small
fixes, but not accept a version that (supposedly) is downwards and
upwards compatible?

What advantage do we get from separating 5 (no code changes) from 3
and 4? In each of these cases, the author is stating that he or she
thinks each version will generate the same results. Either we trust
the author or we don't. 

I guess some users would trust the author unless another user has
sent a configuration report to SqueakMap asserting that the author is
wrong for their particular configuration; while other users will not
trust the author until some other user has sent in a report that
exactly this configuration does work.  But I guess bold users will
trust the author in each of your cases 3, 4, and 5, while cautious
users will not trust the author in any of these cases. Do you
disagree? Do you think some users will trust the author when he or she
says only comments have changed, but not trust the author when he or
she says the code is upwards and downwards compatible?

-- 
Stan