Apparently I missed responding to this when the revealing photos were posted:

As I had suspected, this rifle, 109027, "moves the chains", at least in relation to Mallory 1, the only book I have handy (Mallory 2 and Farmer are buried somewhere).

Highest "Model 1896" WAS 108915, 112 (a very significant amount) lower. And, at that time the lowest "Model 1898" known was 109342, so the gap is closed to no more than 314 numbers.

But, IIRC, Joe Farmer had a refinement in this area as well, so the gap may well be even less, as he was probably unaware of 109027. He calls such arms "border guns" and, like me, finds them very interesting. This particular cut-off point is doubly important because it covers not only the change in date, but also the notable physical difference at the bolt cut.

Was the changeover a clean break, or is there numerical overlap? Could there be a "Model 1896" with the simple bolt cut, or a "Model 1898" with the shroud? I'd strongly suspect not, but who truly knows?

Fascinating hobby!