I think it could be a bit more challenging to find who did 3 or more shows for the same network. Tom Kennedy has done that for two networks.
ABC-Split Second, You Don't Say, and Break the Bank, the latter two just months apart
NBC-You Don't Say, Password + and Wordplay
Trebek did at least 4 for NBC...the two Doug mentioned for NBC, plus High Rollers and Wizard of Odds.