I haven't seen this happen in regular stats, but have definitely seen it in game shape. Although I can't cite any examples of this happening to a healthy player, I know for a fact I recently had an injured player and I was upset because his GS had dropped to 6. The next week it had to my surprise, jumped to 8. I have a suspicion that the 2 number change was affected by his recovery and that it may not be possible in other circumstances for a player to do this, even with high sub levels.