The 1906 is to the 1890, what a 64 is to a 94. Maybe at the factory, back in the day, they were sayin..." What are we going to do with all these 1890 receivers we have out back?"
I guess making the barrel round instead of octagonal, and eliminating the steel crescent butt plate, were cost saving practices. Other than that, how they were blued, barrel twist rate, and chambering the 06 to take all three .22 rimfire loadings, they were the same rifle. Hardly even seemed worth changing the basic model designation. You could say the same, in fact, for the Model 62. I guess they had a lot more integrity back then than they did in 1964 when they kept the same model designation for the Model 70 even though it was an entirely different design.