Here is evidence for naysayers:
http://everquest.allakhazam.com/story.html?story=960
Pertinent quote: "In the old scheme, if a pet did more than half of the damage to a monster, it took half the experience reward."
This post was in 2002; Luclin came out in 2001. However, this post is not the patch note itself; it is commentary on a patch note. Nevertheless, I think it's safe to assume that the patch was around the same time as the post, meaning that for P99, the "old scheme" is permanent.