Sir, this is not my first Rodeo.
I am not referring to the spell effect (added to Allakhazam in March 7th, 2002, along with the creation of Lucy.Allakhazam). I'm referring to the actual spell scroll item. That spell scroll is so rare that no one commented on the scroll itself until 2005.
As stated above, Alla posts from 2002 on Aary page confirm it dropping and 2002 from EQClerics confirm it dropping 2002 as well.
Everlore - October 2001
No Dementing Vision.
Everlore - December 2001
Dementing Visions is listed. As is Koadic's Endless Intellect...
Sounds to me like a late Velious addition or an early Luclin addition. I fail to believe that from December 2000-October 2001 no one discovered the spell across all servers.