Originally Posted by AKX20000
To be fair, 13 episodes could technically be considered a "season".
If you're going by seasonal airings in Japan, but even then it's not always the case and/or doesn't really even work. Not to mention Japan never really seems to have any set consistency with "seasons" for their ongoing shows in the first place, instead just opting to split it by certain arcs.
tl;dr anime seasons are weird ass shit
In my younger, more carefree days, I considered a change in opening song to be the absolute definition of a new season. I now see it's not that simple, but it's still often what I use if there's no obviously better separation point.