My understanding is that all of Trebek's verbal readings of clues had been pre-recorded. All he had to do was watch the game unfold, push buttons, and make appropriate comments.
I'm not sure if guest hosts were permitted that luxury.
I watched an interesting behind-the-scenes documentary on Jeopardy & Alex’s daily preparation. A LOT of work which he did quite well, though he did it for nearly 40 years, and was an experienced show host before Jeopardy.
That’s not correct. Sometimes he would stumble over a clue and after the show, they would record him saying the clue flawlessly and edit the show.