100 episodes for syndication is an urban legend. The minimums are 13 and 65.
Not really. Early on, series sich as Universal's The Sixth Sense
(25 episodes) did not have enough episodes for a syndication package, so it was tacked on to Night Gallery,
would have spent the rest of its time in a vault.
Until the 80s--when studios started packaging syndication blocks of old series which allowed short-lived shows to see the light of day, many one-season wonders (Gidget, The Green Hornet
, etc.) were buried. Other short timers--such as Planet of the Apes
(14 episdoes) and The Time Tunnel
(30 episodes) first earned a second life in the early 80s as TV "movies" made from joined episodes, as they did not have enough for a then-standard syndication package.