No, 202012 is NOT at the "upper end of 1898 Carbine production". That stopped at around 135xxx.

Receiver date is crucial in this case. If 1898 it is a cutdown rifle, if 1899 it could (by something of a major stretch) possibly be an early 1899 Carbine, though I think you have already nailed it when you say that number is surrounded by rifles.

The "C" on the sight certainly stands for carbine, but the mounting holes are identical, so that is not definitive. A 22" length (with no indication of what the front sight looks like) may or may not indicate a genuine carbine barrel, which would screw right into either receiver.

In short, the prognosis does not look good - sorry.