Unfortunately, the mistakes in Cults of Glorantha just reinforces my wariness.
The errors are regrettable but were probably inevitable. They're also localised and not especially extensive. Fixes are easy, in most cases. It doesn't excuse them, but they are relatively easy to deal with. An eratta will be produced. However... a book of the size and scope of 'Cults' is, by its nature, going to be prone to errors. FWIW, the book was submitted to
three separate
external people, all with exceedingly good error-trapping skills, before it even went to PDF layout for further proofing. Some errors were caught and rectified, others were missed even by three sets of Glorantha-wise, proof-reading eyes. There's a hell of a lot of cross-referencing, of spells, allied cults, and various rules nuances, plus attempting to ensure that this version of Cults remains as compatible as possible with the previous editions for MRQI and is consistent with older cults material (and some of that stuff contains errors too). I think CoG is about the most complex book I've written, and it took a long time to prepare, write-up, do the initial check, and then get additional people involved in the post-writing, pre-layout phase.
And stuff still got missed. Its galling, I know: galling for me and galling for you. But - and here's the clincher - books have to be produced to a schedule. You can make that schedule as long as you want. You can go over the manuscript a dozen times, and material, especially in a complex work, will always get missed or overlooked. The RQII core rules, for instance, got combed by myself, Pete, and at least three very good playtesters and proof readers about three times before it was sent in for layout and in-house editing: we still missed things! Its a very complex process. It may
seem straightforward from an external POV - elementary, even, but its never as simple as you think, no matter how long you have to do it.
Anyhow, I am doing the CoG errata. As to Lhankmar and Necromantic Arts, neither were written by me and I've been involved with my own projects to the point where I haven't had time to look at either of them with a view to corrections. I regret that; but I must prioritise, and I know that Matt is also looking at how best to tackle LU and NA.