Yes, watchman, for the watch in question, and the others with Waltham serial numbers in the 9 millions and earlier, they dropped the millions place, and put a "B" prefix in front of the remaining six digits. However, for Balls with Waltham numbers in the 10 millions, they seem to have often dropped just the one and left a seven digit number starting with "0" with the B prefix, but I can't locate my research file on that; I'm rearranging a lot of "stuff." Eventually they settled down to dropping the numbers in the 10 millions and millions place, and using the last 6 digits of the Waltham s.n. with a B prefix.
As for the date, 1900 is about as close as one can come, and it is based on the Waltham production date. However, it is hard to be sure, especially for Waltham Ball production. It would probably be best to say "circa 1900."
Anyway, I'm glad you cleared up the question about the jeweling. Good luck with it.