Ultima 1+2+3: Spellbooks added
Ultima 4: Interview with Richard Garriot added
Ultima 4+5+6: Interview with Richard Garriot added
There were three more updates:
Ultima Underworld 1+2: Reference cards added
Ultima 7 The Complete Edition: Maps, cluebooks and design documents added
Ultima 8 Gold Edition: Lost Vale design documents added
According to the promo news, for Ultima 7 they added a colored map of Serpent Isle and the cluebooks (I think one of them was missing, but don't remember which one).