User blog comment:Kogath/Monster Hunter 4 Ultimate for the Nintendo 3DS/@comment-25143728-20140705204220/@comment-5582528-20140708073655

Charms didn't work on a table system in Tri like they did in later titles. What skills ended up on a charm were strictly percentage based (which resulted in powerful combinations like A+10/B+7 and the highly coveted B+7 OO variants). They moved to tables in P3rd as the number of skills available grew.

Excavated gear is tricky, because they APPEAR to be predetermined combinations of raw/affinity/slots/attributes that are merely plucked out by the RNG a la charms (and the weapon model used is actually determined by the target monster of the quest), but nothing's been conclusive.