Teams need to read or their clues to the cameras, or at least encounter it just in case it was a picture or a symbol or some sorts. After they do, It doesn't really matter if they didn't have the clue in their possession I think
I remembered in TAR 19 in Panama, when they need to find where the pit stop was, they didn't have to bring any proves or sketches that specifically described the pit-stop, as matter of fact, two teams were told by one team's cab driver where the pit-stop was.
I remembered also in TAR 21 when Ryan messed up his Roadblock clue, and he needed another team's clue to figure out how to finish the Roadblock, he didn't get penalized for not having the RB clue at the pit-stop
I think a team will be penalized if they lost their clue, and they went to retrieve another one. Was that ever happened though?