I haven't found patch notes of this being implemented. It may have came with an expansion. I see patch notes regarding the removing of the loop people found casting group beneficial spells in 2003.
There was a forum that discussed this in 2004. One poster had a link to a sony forum of someone who was not happy when Kunark was released because he didn't like the buff restrictions.
Vowelumos
06-11-2004, 03:11 AM
Not sure how this was a bug it was only done this way for what 6 or seven months.
The level restrictions have been in since Kunarks release. The fact that group spells went around the limit was not known untill a bit later when people got into their mid to late 50s and group spells started being used.
I dug up the post below on Casters Realm. it is from May of 2000 and explains the thinking behind the level 39 limit on 51+ spells. (It is a moving limit as I mentioned in my previous post).
<font face='verdana' size='2pt'>Source: <a href=http://boards.station.sony.com/everquest/Forum4/HTML/039117.html><b>Everquest Gameplay Forum</b></a>.<br><br>
As I understand it, a level limit had been put into place for level 51 spells
and higher whereby you can't cast one of those spells on anyone who's lower in
level than level 39. Is this information correct?
<p>Let me say this first, I can see the reason/logic behind your decision in
implementing that level cap. However, I would like to point out how this cap can
be very unfair to a lot of players as the cap is implemented right now.
<p>This is mostly a grouping matter, btw. In my experience, at level 30, I was
able to group with a level 45 and get XP, but not with a level 46. As you,
yourself said before, Gordon, as you go higher up in level, the wider the level
range can be in a group for the lower levels to get XP grouping with a higher
level. In another word, level range in a group for XP purpose is based on a
curve and the higher you go, the larger the range. Base on that, by my
conservative estimate, a level 35 would be able to group with a level 51 and
-- They claim it was from May 2000, unfortunately these boards have long since been removed as sony now has a new forum website. So there's no way to go and verify.