So think of it as 2 seasons?

It's not like it's a new concept in streaming. The Sopranos did it 15 years ago and Breaking Bad did it 10 years ago, and the break was over a year in both cases.

It's probably due to weird contracts or something like that where they have an actor for a set amount of seasons but not a set amount of episodes.

I'm pretty sure there were a couple of time travel episodes in Supernatural that this contradicts.

Also their mother was resurrected and told them about her past.