Nilbog is asking for help in an effort that could solve some of this.
https://www.project1999.com/forums/s...d.php?t=337025
By providing dates and evidence when spells on this list became available on vendors, they will be properly tagged with the correct timeline.
Won't fix everything you mentioned. (if a spell existed for another class, or a spell was removed from a class) but for Spell:Clarity, having the merchant not sell it until May99 would make it unavailable.
There's a spreadsheet a few posts into it if anyone wants to add effort to it.