It is said that Ball felt that jewels beyond 17 or 19 were unnecessary. However, as companies began producing 21 and 23 jewel watches, Ball was willing to market them in response to the demand. Ball also disliked double sunk dials, feeling that they were harder to read and more likely to crack. Very few Ball watches have double sunk dials.
At least Ball kept the name of the original manufacturer, for example I have a 19 jewel watch made in 1912 labelled as a "Ball Waltham". There are "Ball Hamilton" watches as well as others out there. My Ball Waltham has 19 jewels. It has a serial number that begins with "B" - this was the practice where Waltham took the "millions" digit and replaced it with a B for watches supplied to Ball.
The Ball Hamilton 999B appears to be identical the the 992B, except for the plate decoration and markings.
Tom's notes / tom@mmto.org