I recently purchased an old tuba from an estate auction. No case, just the tarnished beast and mouth piece. By looking up the serial number on it, I am finding that it was built in 1891. I am doubting myself. Did I do this right?
I suppose you looked up some serial number table such as this one (page 19+):
and chose the closes matching date. While this will most likely not give you the exact year of production you probably get a good idea, give or take a few years maybe.
I would not doubt that this tuba was from that time period, it does definitely look the part.