Change the event constant to 31, then meet a person in underground, then check if spiritomb spawns.
The constant itself is likely just a record, and won't spawn spiritomb simply because it's 32.
If anything, it's the act of becoming 32 (in-game) that results in a different flag being set. Give that a try.
(Basically, the game doesn't load up the save and check if the record is 32. If anything, going from 31->32 is what triggers a flag, as well as change constants.
However, simply setting "32" as the value doesn't set that flag, and the game doesn't check if it's 32 again)