Your guess originality on model no's 1948 - 1968 will be date code stamped, see link.
Depends on the model, almost all start at 1.
Remington has never made a firearm with the model designation of 812
Remington does make a combo shotgun rifle, the Model SPR94.
No such model in the Remington line.
Shot guns made with the 870 designation was the model of the WINGMASTER shot gun series. This also signifies it is a pump gun opposed to Simi-automatic
Remington Model 11-48 (Highest value) Made from 1949 to 1968: 425,000 were made. $300 for all gauges except the 28 gauge. 300 percent for the 28 gauge.
i have a 1904 Remington single shot over under hammer on left 1904 pattened 1864 when made i would like to no value
Remington has made many thousands of 12 gauge shotguns in dozens of different models/configurations.
probably 200-400 depending on condition
Remington didn't make a pump shotgun until 1908 and that's a model 10.
He used a Remington 870 Police Magnum.
There's very few Remington things you can identify by just a serial but you got lucky ;) That is a Remington Model 1889 made in 1902. Value is greatly dependent on Condition, Condition, Condition, and Condition.