You are the warrior Lone Wolf
In The Plague Lords of Ruel, your mission is to prevent the malevolent Cener Druids of Ruel from releasing a deadly plague virus that will destroy all but their own kind. Of all the warriors of Magnamund only you can thwart their wicked plans
Weaponmastery bonuses are replaced by Grand Weaponmastery bonuses, not added cumulatively (cf. Lone Wolf Club Newsletter 28).
If you have completed previous adventures, already possess the Magnakai Discipline of Weaponmastery with Bow, and have reached the rank of hidden loyalty bonus
(cf. Lone Wolf Club Newsletter 28). In view of this, the
Certain sections direct the reader to use different bonuses when using a Bow, ranging from 3 to 5, if you have Grand Weaponmastery with Bow. This may be the author adjusting the Grand Weaponmastery bonus on a case-by-case basis (and therefore this bonus should be used instead of the standard bonus) or an error (and therefore all of these bonuses should be 5). It is up to you to decide, but it seems most reasonable to follow the first alternative, to replace the Grand Weaponmastery bonus with whatever bonus is mentioned in that section.