Receiver production was kept ahead of rifle assembly, and they were NOT put together in perfect numerical order, so the question cannot be answered with 100% certainty, especially when near the end/beginning of a year. SA was supposed to keep accurate (OVERALL at least) records on the Krag, because royalties were involved.

So far as the 1898 "cutoff" is concerned - that is not just a scholarly question but also a legal one. AFAIK, BATF (your tax dollars at work) uses 152670. Whether that is "right" or not, it would probably be prudent to treat it as such, if selling, shipping, etc.

Now, as to why 152670 is a harmless antique, and 152671 is a fiendishly evil device deserving full regulation, write your Congressman (or perhaps, try to elect a new one)!