[Uatu]

The switch to 2e (for example, specialty priests were a 2e thing in the first place (although 1e Greyhawk and Dragonlance had something like that anyway); Forgotten Realms had a lot of variant rules for this, though (different experience tables, for example)).

I dunno if we need to define 1e vs. 2e (or should we?)... Well, I guess we might have to in terms of timeline. In general, 1st Edition Forgotten Realms follow the 1st edition rules - so you see half-orcs, monks, and old-style rangers and bards (movement/range is given in inches, which should give them away). Various deities exist, but their priesthoods are not as fleshed out as in 2nd Edition. Most FR material is 2e, with kits (i.e. Rashemaar berserkers), specialty priests (i.e. Helm's watchers), new classes (i.e. the rather useless Harper class), and so on. To match the changes (following the rule changes), the FR background stories have some large event that changes everything (was it the Godswar for 1e to 2e?)...

The Monstrous Compendiums I think are a bit unfair in ascribing certain monsters to Forgotten Realms or Greyhawk - since a lot of these monsters were in the old 1e Monster Manuals or Field Folio, anyway. The Dragonlance MC is probably the most accurate in terms of campaign-specific monsters (of these three, anyway). So it is rather difficult to say for sure what monsters are FR-only; I can think of Tressym, Lock Lurkers, Baneguards, Weremoles, and the like.