A nonmember's moderation action should take priority over *_these_nonmembers.
The current behavior for nonmember posts is to first consult the legacy (accept|hold|reject|discard)_these nonmembers in order before the nonmember's moderation action. This can cause issues. For example consider an address in MM 2.1's accept_these_nonmembers which also matches a regexp in hold_these_nonmembers. Mailman's import21
will import the address as a nonmember with moderation action Defer
but will import the regexp to hold_these_nonmembers. This results in MM 3 with a post from that address being held, where in MM 2.1 it was accepted.
In any case, a specific nonmember moderation action should override any *_these_nonmembers hits.