So a little sleuthing here.

55295 is first hammerless built in 1888
Rebound patent # 412340 issued Oct 8, 1889
59123 is last SN for 1889
1889 saw 3018 guns built so last two months would account for 503 guns + or -

Unknown quantity of existing inventory to be expended to use post Oct 8, 1889 but maybe the 500 guns could have used it up (or not but probably close) by end of year

So 59123 has potential to be near the end of Parkers with non-rebounding internal hammers.

Anybody got one near 59123 to have a look??

Cheers, Jack