If the GUID is null, does the core automatically assign the next available GUID, or does it still have to be specified? Like a nextGUID field? I was thinking if it was NULL the core could automatically assign the next available GUID (updating the creature DB record to reflect it) before actually spawning it, since these are unique to the core and not the actual game, and could be different on each server without impacting the game?
For example, any user generated GUID between or above a certain threshold wouldn't conflict with core VerifiedBuild assertions: core GUID 1-750,000 user GUID 750,001-100000.