Yes I am having trouble finding a hard date myself. It seems we know it was before 01/2000 and 10/1999 patch makes the most sense to me. I guess tailoring was part of the quest as well. Brother Qwinn and Brother Z are both confirmed spawning and dropping the robe on Green as well
"Skill in tailoring is no longer required to craft The Robe of the Lost Circle ." June 2000 patch the stats get a boost that patch date as well.
https://everquest.allakhazam.com/his...es-2000-1.html