Delta Drive, Delta Trust & My Drive · Search, notes and versions
Why can't I keep versions for less than three months, or longer than the folder above?
Short answer: Three months is the minimum so nobody loses a version they need, and a folder can't keep versions longer than its parent. Shortening shows what would be deleted before you save; current copies always stay.
Two rules. Three months is the shortest we offer — below that someone loses the version they needed, and going back is the whole point of keeping them. And a folder can be set shorter than the one it sits in, never longer: longer options simply aren't offered inside a limited folder, and the screen says why.
A year is the longest fixed window. Forever inside a limited folder means "as long as the folder above allows", which is why it's always available.
Shortening is a decision to delete, so the screen shows how many copies would go and roughly how much space that frees before you press Save. The current copy of every file always stays.