It appears that the HeroQuest:Glorantha rules on Spirit Magic neglect to mention (explicitly) that members of traditions who are not yet also members of a spirit society have their Spirit rune ability limited to (one presumes) 19W. The rules to specifically say that spirit society members are no longer limited:
HQG p. 136
“You may increase your ability in a charm or the spirit society keyword without limit.”
Although nowhere in the previous section does it mention what those limits are.
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