Yes, I agree with correcting the dealer and backing up the action. There is no way Player A gets to take his 100 back, no matter what. If I understand the situation, Player A's declaration, or question of raise should be firm to the minimum of what? You say it's spread limit but you fail to tell us the amounts.
I will modify my answer from last night. Player A should have been able to raise, because Player B made a full raise. Player C's all-in was not a full $40 raise but, in limit poker, his raise counts as a full raise because it is more than 50% of the $40 raise he is facing (the all-in action was $36). So, Player A should have been allowed to raise to a minimum total of $140.
I guess it would be unfair to hold Player A to a raise, because he didn't say raise, he just asked if he could. However, I see no way to allow him to retract his call after he realizes that Player B is going to raise! That, in my opinion, would be a bad call by the floor.
Bottom line: I agree with Tristan, Option A is better than B, but, they are both better than letting A retract his $100.