Meh, I recovered an old copy of my board to pin that side plate change you mention. That is specifically an 1896 model change. The plates with the screws at the crease (1892s) is model 1892 only. Late 1892s have early 1896 parts though so it gets murky.

1896 Mar 10: Thickness of upper half increased and cartridge rib lengthened.

The change to the side plate. Listed with all of the 1892->1896 changes.

The other visible different I mentioned:

1899 May 5: Rear upper corner rounded.

The barrel/receiver fillet was done in July of 1899.

Fun with parts.