[diggan]

What about if the FTC discovered information that they had no idea about existing at the point of merger, would it be OK for them to go back and reconsider the merge if that's the case, with this new information?

That's how the article reads to me at least, that the FTC wasn't aware of the documents/information even existing, so obviously they couldn't ask for it at the time (an unknown-unknown, rather than known-unknown).

Overall, I feel like the article itself is withholding information about exactly what information is now known by the FTC, so hard to judge anything here.