Just adding my voice to the chorus, for whatever it may be worth: I also assumed, based on previous events, that I'd be able to use my tomes after the event ended, and am stuck with a few hundred across multiple characters. On one character I got the last 20 I needed from a Prae run that finished two minutes before the event expired. If you could still earn them right up until the cut-off with no time to actually spend them before it ended, there should be a period afterward to exchange them.

I read the event page multiple times over the course of the event without noticing the disclaimer. I wasn't aware of it until this evening when I started searching for why the exchange wasn't available. I accept my share of responsibility for failing to see it, but given the number of people (including everyone in the aforementioned Praetorium run) who weren't aware of the cut-off, they clearly could have and should have made it more obvious.

I am not of the opinion that they are under some kind of obligation to reopen the exchange for people who didn't see the warning. I am absolutely of the opinion that doing so is the right thing to do.