But you may check for it like this: fire up the game, open the character screen (the one which lists all the detailed stats for a single character) and right-click the experience or the attack and shoot bonus fields.
If the Grayface's patch is installed, you will see which level are you eligible to train to and how many XP are remaining to the next one (if you clicked the XP field), or the recovery times (if you clicked the attack or shoot bonus field).
If it's not installed, you won't see any of these. Please note thta this is only from the top of my memory, so it'd be worth checking both options.
Finally, if the Grayface's patch is truly installed, you needn't worry about any other patches, because that patch actually contains all other patches made for MM6 (i. e. Mok's).