My personal observations, FWIW: Unless, I am comparing 1896 & 1898 plates side by side or measuring the front-edge tenon with a vernier caliper, it is very difficult to identify a model 1896 side-plate.
Also, BTW: If you have Poyer's book, he gives incorrect dimensions, on page 104, for the increase in model 1898 side-plate tenon thickness. The increase was from 0.130" to 0.150" (not 0.230 inch to 0.250 inch). My 1898 side-plates actually measure 0.155" at the tenon.
Significant changes per Mallory and Brophy:
The 1898 side-plate tenon increased .02 inch (from the 1896 tenon).
High polish on inside of 1898 plates stopped Nov. 28, 1898.
Rear upper corner of 1898 plates began being rounded, May 5, 1899.
So, if I have it right, an 1896 side-plate will have: 1. A thin tenon, only 0.130" thick. 2. There will be a higher polish to the 'browned' (blued) interior finish (fewer tool marks). 3. The upper rear corner of the plate will have a 'sharp corner' and not a 'rounded bevel'. (Early, 1898 side-plates will also have the high polish interior finish and lack 'rounded bevel').
Attached photos: 1. comparing 1896 (Left) and thicker (.155") 1898 tenon. 2. caliper and 1896 plate with .130" tenon. 3. subtle high polish interior (Left) compared to dull interior. 4. early 'sharp corner' on left and 'rounded bevel' on tang of later 1898 side-plate on right.
