Between expansions quests change , different questgiver, different turnin, new quests or removed quests like training spells.
For example https://tbc.wowhead.com/quest=1470/piercing-the-veil got removed in 3.3 when the reward spell was moved to a class trainer.
I think we should be able to keep separate timelines of the database for each major revision , aka expansion.
So we can still copy classic to tbc or tbc to wotlk to have a foundation but we are able to make adjustments if need be.