> Forget original purpose, is there presently a bug or not?
Yes, there is a bug. Accounting rows inserted as part of an aborted transaction in n_ins_since_vacuum is not correct, since the same rows are being accounted for with n_dead_tup.
So why is it important we not account for the aborted insert in both n_ins_since_vacuum and n_dead_tup?
When would you ever add them together so that an actual double-counting would reflect in some total.
You aren't upset that n_live_tup and this both include the non-aborted inserts.