The errata on this page is very incomplete because the errata for True20 Adventure Roleplaying and True20 Companion were being maintained by True20 editor and contributor Erica Balsley on her website, which no longer exists. The only other source of collected errata that I have found is the following archived and locked thread in the True20 Forum (to which I contributed when the thread was still active, and from which Erica derived much of her material): http://roninarmy.com/true20-forum-archive/viewtopic.php?f=2&t=360
A few comments that aren't strictly errata appear below:
pp. 24-30, Optional Rules: Heroic Character Archetypes: These benefits apparently are in addition to the normal benefits of advancement. This will make the heroes somewhat more powerful than their level would indicate. These rules would mesh better with the standard True20 rules if they were rewritten, perhaps as optional feat trees, instead of adding their own unique rules set.
p. 31, Renown: Reputation Qualities already appear in the core rulebook.
pp. 33-34, Divine Aspects: The Role of the Gods: The True20 Freeport Companion (p. 22) presents an alternative, using feats rather than core abilities.
pp. 83-86, Ritual Magic: The True20 Freeport Companion (pp. 42-46) presents ritual magic rules almost identical to these, but using a Knowledge (forbidden lore) check instead of an ability check.
pp. 86-93, Fear and Terror: The True20 Freeport Companion (pp. 26-28) presents alternative rules for madness and corruption.
Monsters by Type (and Subtype)
See the monster type index in my errata for the True20 Bestiary, which includes all new creatures from the True20 Companion.