These four are all valid ways to spell the "rebase -i master" step.
and I think it is sensible to expect
(1) they all behave the same way; or
Yes. My reasoning is very simple: a rebase is a rebase; it should not
write "checkout: " messages to the reflog. Therefore, the @{-<N>}
will ignore it; for the purposes of checkout -, the rebase event is
inconsequential.