When I was editing Glorantha writing for publication in the French fanzine, my take on it was that the writers could do what they liked except to directly contradict the canonical sources such as they existed at the time. Most of the time I would try and find a means to reconcile what the writers wanted with the canon, usually successfully, although there were times when that was not possible.
There was of course not much that one could do about being Gregged by any subsequent official publications, although one would nevertheless make brave attempts to avoid any such fate. :D
People should bear in mind though that there are some areas where the Gloranthan sources are deliberately self-contradictory, or have been retconned/Gregged in some more complex way than just flat out replaced, so that adding another layer of contradiction might actually be a positive instead of a negative.
Writing or publishing fan material also offers a lot more leeway than writing professionally and/or officially for Glorantha however, because official Gloranthan materials must (ideally) not only be consistent with the current state of the canon and with Greg's more current insights, but it must also in very many cases become part of the canon itself, so that it will therefore come under far more scrutiny and focused attention from the-powers-that-be than any kinds of fan material are ever likely to be subjected to prior to their publication.
>From the fan writing point of view, creating fan materials that are deliberately divergent from the canon can be fun, and only subject really to the whim of your editor.
The status of the 2nd Age Mongoose materials in relation to the 3rd Age materials of classic RQ and HW/HQ is a complex one, because the world itself has actually changed somewhat drastically from 2nd to 3rd Ages. There will obviously be some undesired discrepancies due to editorial/authorial slips, but some of the discrepancies where MRQ materials can flatly contradict HQ ones may be perfectly deliberate on the designers' part, whereas some others may be explained and reconciled for some unpublished reason or other, while others may exist simply as game artefacts because RQ and HQ are different games.
As GMs and players, the received MGF wisdom concerning contradictions in the sources is to just accept that all the contradictions are true, and then to either completely ignore them as boring and irrelevant, or alternatively to have as much fun as possible by deliberately focusing on them :)
Julian Lord
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