Some of those early season bucks may very well move to new territory once the velvet comes off. Also concider the possibility of the change in habitat/food source as fall comes on, as compared to when you were getting all the pictures.
For instance, my buddy also gets lots of great buck pictures before the velvet is shed. About the time the velvet comes off and the soybeans leaves begin to turn, just like a light switch, they dissappear. I shot a buck that my buddy had several pictures of this fall. The buck had moved 1.5 miles from the place where he getting his picture taken alot, to where I shot him.