My friend recently loaded up her world, and the world looks like it may have been corrupted.

I spawned in the world spawn point, with none of my loot that I had worked for the past week to get, then when i reached our house, there were rooms missing from the house that were there the last time we saved, but not there at the time i joined the world. The owner of the world and my other friend, who had been playing on the world well before i was, had their loot, but their friend and I did not. Some of the changes that I made to the world remained unchanged, but a lot of the changes were reset or half-made. I really can not comprehend what happened other than the most recent world save was combined with a previous world save from about a week ago. A lot of the rooms we made were dug out, which happened after I joined the world, but it did not have the blocks placed in it. For example, the enderchest we placed had the outline of the block, but it was not there, but the other enderchest we placed, only the two people had their items in it, but me and the other player did not. Very hard to explain, and very hard to comprehend.