Misuse of the "Revert to" in Pool History

I don't know how to start, well, here I go.

I removed several works on " Wow, That Was Fast" pool by mistake after I clicked on the "Revert to" button on the Pool History. Before that, I'm checking my account's records and noticed that there are some blank spaces on the "Changes" column of my Pool History, thus I clicked on the "Post Count" beside a particular blank space, and then clicked "Revert to". I'm hoping to know what are those blank spaces. Unfortunately, I admit that I made a mistake so I humbly apologize since there are so many entries removed in the process.

The “Wow, That Was Fast” pool has already been fixed by Unbreakable, but if you mess something up again, you can easily fix it yourself by going to the pool’s history, for example, and then clicking the “Revert to” link on the entry below yours, effectively reverting the pool back to how it was before you messed it up. Same goes for tags and notes.

Thanks for the tip.

I wonder why pool history doesn't have an "Undo" option like tag changes have.