Restoring Invalid and Deleted books

[albie_of_nonfic]

While adding or updating books, I have come across several books that already exist on the system but have been set as Invalid or Deleted. The books appear to be legit (they are books, with ISBNs, not anything that could be deemed to be 'not a book'). Going through the edit record for these books does not show any reason why (some have been tooled around with endlessly by Amazon, while others are unchanged since listing).

(1) Is there some glitch or issue that causes this? If so, how do I identify this? (this seems to be common knowledge, but I am new to this and don't know)
(2) Is it all right to flip these back to Public?

Another book (Hitler's Revolution, by Richard Tedor) seems to have been set as Invalid by admin, for reasons that are not clear to me (I presume it has been effectively banned, as it is deemed to be controversial or offensive).

(3) How do I identify books that have effectively been banned by admin? I don't want to flip one of these and get terminated as a librarian.

[Scott]

If an admin has marked it invalid it will say so, and you won't be able to change it back.

For others, use your judgement. Yes, there are many glitches marking books invalid, or giving them invalid status even though they are still public.