They reuse numbers for what I call "marketing
numbers". For example,
with a LaserJet 8150dn, the "8150" is a "marketing number" and not
the
actual HP product number, which was C4267A. As far as I know they've
never actually reused a product number.
I know that's no consolation when you search for "HP 5480" for that
product, and get printers or supplies with that "marketing number"
instead.
I get irritated when I search for HP9100 (meaning the first desktop
scientific calculator thing) and get hits for some modern-ish
printer/scanner. Admittedly that is a 9100C (the calculators were
9100A and 9100B), but...
I seem to remember that there are at least 5 different HP10 calculators :
HP9810 (which was called the 'Model 10 Calculator')
HP10 (or HP10A) : A simple handheld adding machine with printer
HP10C : The simplest of the 'Voyager' series. Scientific, programable
HP10B : A simple financial machine
HP10B-II : An upgraded HP10B
-tony