There was someone on facebook who was questioning a 1901 cartouched 1896 not long ago. My guess would be they had some 96 receivers still in the system when the boss said in July 1898, "We're going to start producing 1898s." Come 1900-1902, with it being obvious there was a new rifle on the way, time to tidy up accounting so that royalties could be paid. I'm sure they still had the tooling to cut the bolt handle recess and flare still on hand.
"I have sworn upon the Altar of God, eternity hostility upon all forms of tyranny over the minds of man." - Thomas Jefferson