To begin, as is stated on the front page, credit for most of the data goes to the Slick Productions FF4 R&D Forum, in general.

I'll list everyone who has data contributed on the site in alpahbetical order, along with the data(docs) they contributed:

Deathlike2: Elemental Ref. Guide, Attack Algo, Avenger Sword, Bow & Arrow Data, Magic Algo, Sylph Summon, (Part of)Random Spell Notes, Caignazzo, HP% Spells, Monster Spells, Back Row Bugs, and the entire "Statuses" section

Dragonsbrethren: Window Data, Weapon Bits, and Item Drops(FF4ET)

Edea: Lv. up data, Magic list IDs

Entroper: Monster Reference XLS

JCE3000GT: FF2US Hacking Doc, Pointer Data, Chest Offsets, FF2 Music, FF4 Music, FF2US Item Drops, Monster Img Data, and Pinkpuff Data

Paladin: Item Compendium XLS

Phoenix: Shadow Party Data, Event Offsets, Element Data, Attack Sequence Differences, Weapon Changes, Spell ASM, (Part of) Random Spell Notes, Atk Sequ Group Data, Attak Sequences, Enemy Condition Indicies, Command Disabling by Status

Zyrthofar - Item Drops(FF4/2us)

Bond697 - Monster Location Guide