The action declared in the case of Ray of Frost doesn't have it's outcome change if the player includes more words than "I cast Ray of Frost at that target."Where as in the case of Recall Knowledge there are different outcomes that rely not on declaring a different action like declaring Acid Splash would be, but on whether the player said "I Recall Knowledge about that creature," or something like "I Recall Knowledge to figure out <specific detail the player is guessing about the relevance of>."
A centipede swarm has resistances bludgeoning 5, piercing 5, slashing 2. A shortsword deals piercing damage, but has versatile P.
Thus in the case of striking a centipede swarm with a shortsword there are different outcomes that rely not on declaring a different action like declaring a strike with a shortsword or a strike with a hatchet would be, but on whether the player said “I strike with my shortsword” or something like “I strike with my shortsword for slashing damage <which the player is guessing about the relevance of>.”
So, do you allow the player’s successful attack roll to be mitigated by his poor choice not to use the versatile quality of his weapon, or do you instead decide for him that he selected the more effective damage type?
In this case, the player, when he made his successful Recall Knowledge check, realizing his PC has a shortsword wanted to know whether piercing or slashing damage was more effective, but his GM told him about centipede venom instead.
So you are saying that GMs have recall resistance.