Hello Eleanor! thanks for checking out the game - this very point came up recently, and will get addressed in future games. Your no longer Rank up after 12, or 20, if your table prefers this...but you still advance per the other bonuses. of course, doing this forever, makes your Rogue far too strong, but I would move advancement towards tarnish points (and I encourage creating your own tarnish skills!) and aspects.
Hope this helps