explains that dating pianos purely on the basis of numbers is not always as simple as it seems, and if you can post photos here to show what the piano looks like, I may be able to give you a rough date. If you want to search inside the piano for clues, have a look at
There is useful general information about upright pianos at
Email via my website.
If you find old references or links on this site to pianogen.org, they should refer to pianohistory.info