It's implied that in reality in which Frasier is dating Monica, that since he did not help Daphne carry the bags into the house, he never found out the recipe for Niles' Valentine dinner had cumin in it. Because in the reality when he did not date Monica, he noticed it and told Daphne that Niles was allergic to it. This prevented Niles from getting a rash in that reality.
However, Daphne told Frasier and Martin that it was a complicated recipe and she was going to practice it and have them be her guinea pigs. So she was going to make the recipe and have them eat it. It's rational that Daphne would have done this in either reality and then Martin and Frasier would have realized it had cumin in it when they ate it.
Daphne never mentions the recipe or the cumin. As the men didn't know about the cumin when Niles has the reaction, it is obvious that she never made it or tested it on them.
However, Daphne told Frasier and Martin that it was a complicated recipe and she was going to practice it and have them be her guinea pigs. So she was going to make the recipe and have them eat it. It's rational that Daphne would have done this in either reality and then Martin and Frasier would have realized it had cumin in it when they ate it.
Daphne never mentions the recipe or the cumin. As the men didn't know about the cumin when Niles has the reaction, it is obvious that she never made it or tested it on them.
Daphne mentions Niles' allergy for scallops, but previous episodes show Niles enjoying scallops with the meals he has.