I was going to put this under general RM, but then I thought "I don't run Lores they way they are supposed to be, so maybe this is a better question for House Rules." So first, let me describe how I handle lores.
The number of ranks represents how much you have learned. More complicated topics require more ranks. The bonus is only used to determine if you remember info at the drop of a hat, in pressured situations. Otherwise, I judge that you eventually remember or look up the facts. (I might have player roll to determine how long that takes, but success is automatic.)
So, if you do things like this, or can imagine doing so, how would you handle specifically what knowledge the character has per rank? For instance, would one rank in Herb Lore give you general information about all rarity 1 & 2 herbs, or general information about all rarity 1-3 herbs that grow in your home region? Or maybe you spend that one rank(ie the in-game time it took to study) to learn everything there is to know about one rarity 7 herb?
Depending on how you divide up the knowledge will determine when you have nothing left to learn.
What about the less academic skills? For instance, in my current game I have a Leader, and he is pumping the heck out of one of his Tactics. Or should this just be limited by the decreasing bonus already in the system?