According to Maxene Fabe's 'TV Game Shows' book, ABC had a winnings cap of $20,000. CBS had a cap of $25,000. NBC had no cap, but the contestant was limited to two game shows on that network. The contestant had to wait two years in-between shows before they could appear again (regardless of network). On the daytime version, 'Wheel of Fortune' first had a five-day limit (later reduced to three days). On Card Sharks and Password Plus, the contestant retired after seven matches.
Nowadays, all winnings caps have been abolished, especially for the syndicated 'Wheel' and 'Jeopardy!' The contestant can only appear on a maximum of three shows in a 10-year period, with a one-year moratorium between each show.
As for Judy Bongarzone, she won her $64,000 in a 1976 NBC promotional sweepstakes--not as a contestant on 'Wheel'.