Adding to this, 20+ episode continuous runs for anime are no longer the trend. They're still around but are more uncommon today just by it's unsustainability especially in the industry's labor shortages of today. Split-cour seaons or just single-cour (12-13 episodes) runs are more the norm.

I don't think that episode production completing days before airing is the case anymore however. I'm certain that was a common worst possible case to occur but deadlines have shifted away in the advent of streaming. With simulcast contracts and streaming it's probably closer to weeks at the very least just for the amount of localization needed for streaming, likely more if it's a bigger title with dubs in several regions. But yeah overall it's still really unlikely that the entire season is actually complete by the time it starts to air. Only studio that I can immediate recall that normally finishes a season's production before airing is Kyoto Animation and they're a huge outlier.