Can PNY really do this?

I OC’ed my PNY Ti4600 and killed it…I’m RMA’ing it to PNY, however in their return E-mail to me, they said that they can determine if the card was OC’ed and it will void my warranty… Can they really do this???
I WAS able to get back into Windows and change the clock speeds back to Default before I pulled the card out.