The engine number falls in the late 1913 era, so could be one sold in 1914. The frame number is stamped on the side of the lug that the transmission bolts to. Frame and engine numbers would not match, even from the factory as components were built in batches and put into stores till assembled. Numbers for 1913 would be 6940-12500 and 1914 12500-19000 or there about.
I have seen dates engraved on the timing chest cover, but not the crankcase proper (or not yet anyway.) Covers can be changed between engines so the engine number is more reliable. A lot of parts interchange between the years, as you are probably finding out!
-Doug