You have mixed serial numbers which is not uncommon with U.S. marked SAA's. Arsenals of the time would disassemble revolvers putting all the hands in one bin, frames, trigger guards, etc., in their own bins, then reaasemble not worried about mixing serial numbers.
Serial number 12691 on the frame and 12700 on the trigger guard are both within production year 1875.
The dates you are looking at are patent dates, not the model or year of the firearm. There was such a thing as 1872 models but those were open top frames, a different model.
You have a 1873 model Colt, P model , Single Action Army, 7 1/2" barrel. It is missing screws, ejector rod & housing, and has homemade grips that are not well done. Looks like traces of nickle that was not standard for a US marked SAA. So it might have been done later.
The holster ressembles a US flapped holster but the latch in your photo is not clear, doesn't look right. If it was an original gov't issue holster that adds to it's worth.
I like Colts and if you want to contact me by PM.