Other than the 1899 250-3000 Rifle pg stocks, all of the other pre-WW1 1899s with pg stocks have had the distinctive curve, "wave", shape on the bottom of the pg. This is the same design as the early Marlin lever action rifles with pg stocks. I can't exactly tell from the picture, but the bottom of the pg appears to be straight, rather than the curve/wave shape.
I have around 80 1899s with pg stocks and all of them have the curve/wave on the bottom of the pg.
