Scott, I have several Walthams in my pocket watch collection, mostly railroad grade but a few lesser models.
Your above piece has a really nice 'fancy' hand painted dial and matching fancy hands.
The caseback with the '20 Years Warranted' refers to the thickness of the rolled (filled) gold. It was guaranteed to last at least 20 years.
If I read the serial number correctly (16289692) I can tell you it is a grade 220, model 1894, made circa 1907 and has 15 jewelled bearings and the size is 12S. Run quantity was 2,000, total production of that model was 817,280.
By the way, the 'centre wheel' is solid gold, all others are brass!
I have some watch cases with only 10 years warranty (the minimum) and they still show no sign of 'brassing' or wearing through to the brass case.
A cracker of a watch you have, with family history to boot!
Regards,
Jay.