Just read this:
Default Days before Permanently Deleted
By default, posts, pages or comments in the trash will be permanently deleted after 30 days.
(Each item will be deleted 30 days after it is sent to the trash. If you trash things at different times, you may find some items are deleted and some remain.)
How to stop wpress from deleting my trash automatically?
That's maybe the reason I can not find some customers posts/pages back.