Also ridiculously rare, a genre show surviving on one of the broadcast networks.
Season 4 of Alias also ran non-stop January-May. The later Lost seasons also all did runs from Jan/Feb-May. They were both on ABC. It’s just something channels can do when they have a show that is very very serialized. They found the ratings did better than having 4 weeks on, 2 weeks off, 3 weeks on, 1 one week off blah blah blah. People would forget what was going on or not be able to follow the storyline very well and just give up. Just knowing your show would be on that day/time without fail was helpful.
Still to have enough in the can to run nonstop like that, they STILL have to start filming in July. Usually the writers go back to writing in June. You’ll note at the late July Comic Con last year that they had already resumed filming. Once films 8-9 days per episode.
However, Once can only return in January IF they move days actually. You just can’t run straight through on Sundays because there’s too many awards shows and sporting events to pre-empt for. I think moving days/times would be a bad idea. But we’ll have to see what ABC decides.