an anachronism in Gravity's Rainbow????

[JOEYDEVIVRE at delphi.com]

Reading GR I've always been impressed with the accuracy of
the period props, brand names, movie references, etc.
However, the noted Joycean D.J. Schiff has pointed out
a reference on p. 583 to the "Oh Boy" pinball game, which
he says was not manufactured until the mid 60's, 1962 or 1964
or thereabouts.  Could it be that Pynchon's fact-checker
let one little anachronism slip through?