Most all the 70 and 71 440's that I've have were cast in 69.
Had a numbers 71 GTX with a 69 casting.
I sold a G440 HP 2 motor several years ago that was cast 4 26 71. Had 6 pack rods, steel crank, 346 heads. I do not recall the exact assembly date, but it was sometime in May of 71.
I currently have a '70 440 motor cast in May of '69 that was not assembled until October 31 1969.
I'm guessing they probably cast 440's in batches and used the stockpile over multiple model years, then cast another batch when needed.
By '70-74, the annual sales of the big motors was probably shrinking, so a casting run probably lasted awhile.
