Omissions in earlier books were indeed resolved in later ones, and of course many extensions of the system, also many new spell guidelines, introduced.
Some significant examples are:
- HoH:S p.113 box Wards and Penetration following up on forum discussions, finally being decided by the line editor
- AtD p.59 box Leap of Homecoming and Regiones
- TME p.107 box New Guidelines for Instant Transportation (see also errata for that)
- TtA following up MuVi errata on p.75 box Alexander of House Ex Miscellanea's Wizard's Vigil and, redundantly, p.137 box Ferra of Bonisagus' Day of Communion
- TME p.101ff The Superb Scrinium implicitly replacing, but not invalidating HoH:TL p.101f Twinning the Tome with its unsatisfactory big "+5 intricacy" modifier
AFAIK none of the many, many later additions to the system, however, have ever tried to sneak in errata to core book ArM5 without saying so. That would also be a hack student's way to introduce corrections, and unworthy of ArM5.
HP p.82 Hearing the Tearing uses T: Hearing, and doesn't follow its description on ArM5 p.113f Magical Senses. The HP p.82f Assassin's Bell and Listen to the Bells don't even mention this contradiction, and certainly don't make it an issue: so it is clearly an oversight. And these may happen everywhere.
Cheers