https://everquest.allakhazam.com/history/patches.html
Nothing was done to buff pets between the moment epics were introduced and late 2003. I found this patch though, which is most probably the one you're referring to:
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March 25, 2004
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Headlines
-Refining some DX9 functionality.
-Some adjustments have been made to pets.
-Some general bug fixes.
-Added a new rogue discipline line, Assassins Strike. The tomes can be found in the East Commonlands and the
Plane of Knowledge.
DirectX 9
-The center of collision for all players
-We have made improvements to position processing which should alleviate some of the problems related to getting
stuck in geometry.
-Improved collision and movement when near overhangs.
-The auto-duck mechanism is now an user-enabled option. It can be set in the General tab of the options window.
This feature forces your character to duck automatically to get into small places. If set to off, you will need
to manually duck to enter those places. It is "on" by default.
-Warping of very small NPCs (e.g., giant rats in Qeynos) has been resolved.
-Rain now has visible weather.
Pets
60+ player pets have been improved in a number of ways. Most notably, the effects of pet foci will be more
dramatic as a player progresses with more powerful equipment. There have also been a number of inconsistencies
between different tiers of pet foci that have been fixed. All of the existing foci should never show a power
decrease in any aspect when upgrading from a lower tier foci to a higher tier foci. The most dramatic changes
in pet stats are in the following aspects:
Level - Most tiers of Foci will add one level to the pet.
Max HP - Most tiers of foci will add max hit points to the pet, some tiers are more dramatic than others and follow
a similar rate of progression to player characters as they gain equipment equivalent to the pet focus items.
Mitigation (AC, Agility) -- Most tiers of foci will add mitigation to the pet. Some tiers are more dramatic than
others and follow a similar rate of progression to player characters as they gain equipment equivalent to the pet
focus items.
Damage Output - Generally the pets did not receive a significant change in their damage output, although there are
certain pets that have had their max hit and offense increased.
Overall, the player pets have received a significant boost. There are instances where you will see no change in a
specific aspect of a specific pet. For example, the Rathe’’s Son pet summoned with Minion of Eternity has not received
an improvement in max hit points, but it has received a significant mitigation improvement.
These changes affect the pets summoned by the following spells:
Ward of Xegony
Child of Ro
Servant of Marr
Rathe’s Son
Legacy of Zek
Saryrn’s Companion
Child of Bertoxxulous
Spirit of Sorsha
Spirit of Arag
The most profound changes were made to the magician pets as they were most in need of improvement to maintain class
balance. Beastlord and necromancer pets also received upgrades, but not of the same magnitude.
You need to take into account the several tiers of pet focus items that affected 60+ pets and gave beefier pets than your regular Johny Magician w/o any focus item could ever summon