He does not know whether the original blue Finesse was a Layered Finesse or not.
Thus, he must mark his slot 2 card as the red 1 or the blue 2.
If his slot 2 is a red 1, then Alice's clue was a Layered Finesse, and Cathy's clue was a "normal" Play Clue, meaning that Bob has a blue 2 on slot 3.
If his slot 2 is a blue 2, then Alice's clue was a regular Double Finesse, and Cathy's clue was a Queued Finesse, meaning that Bob has a red 1 on his slot 1.
In any case, Bob must blind-play his slot 2 first, and after seeing what it is, update his notes accordingly.
Note that it is also possible that Bob's slot 2 is an unrelated playable card, like a yellow 1. This would be unlikely, but if that were the case, it would mean that he has another playable card on his slot 3. However, by default, Bob knows that he does not have to consider this kind of thing. (If it does happen, he would retroactively update his notes.)