If you look at the top of the post it shows you how to see what grimoire you're missing. You were given 35 Pts out of 45 Pts for your warlock grimoire card so far. That is correct, because you can still get 10 more grimoire for the last two levels of Crucible Kills as a Warlock. The max without getting Ghosts from Terminus and Kings' Watch (future DLC areas) is 2880. You have picked up those ghosts, so you are going to surpass the maximum grimoire score on Xbox. Does that make sense?