I’ve noticed gems in gear sometimes don’t display their actual value.
For example: Topaz in my pants displays “Gain 4 Focus on Focus Use”, but I actually gain 13 Focus on every use.
In another pants the displayed value is 5 Focus, but I actually gain 10 (so not only are the values different, higher displayed value does not mean higher actual value).
Also, before topaz in pants was changed in the hotfix, they displayed 8% and 9%, respectively, but the “lesser” value generated more Focus even then.
I also have a weapon where topaz displays “Gain 3% Focus on Damage dealt”, but from testing I can tell that is only 1% (with 602 max Focus, I only generate 6 extra Focus).
I have not tested other types of gems.