The first one ever was the Sunday repeat of the first C1 episode. I stumbled onto it by accident actually. I didn't watch the whole season because I had forgotten about it but I did manage to tune in for the finale. That was an accident too. I remember being overjoyed that Adrienne won and so happy for her even though Elyse was otherworldly to me. Anyways, I didn't watch anything from C2 and C3 but I began rewatching it with the Zodiac shoot in C4. I fell out of loop again and then watched the Seven Deadly Sins episode. After that, I've been watching them all since. So technically speaking, C5 was the first cycle I watched every single episode during their original airings.
And during C7, my interest was elsewhere for two weeks apparently because I missed the Michelle/Amanda eliminations. I think those are the only times I completely and totally missed any episodes.