I'll think about it some more -- my current best idea is to track how many players in a given datacenter have used the recipe; once it's up to X number of players the recipe is revealed after Y duration.
I hate having arbitrary values, but in my head X=5 and Y=1 month.
So... ferocity scales based on character level (https://wiki.guildwars2.com/wiki/Ferocity) - does concentration and expertise scale the same? Since precision scales differently... and what about vitality? D: