Its very common, depending on how you drive. The factory alignment specs for the Z06 include a bit more negative camber than the regular Corvette, which helps maintain a better contact patch under hard cornering such as during autocross or road courses. However, such an alignment setting will cause the insides of the tires to wear faster under normal highway driving. Solution: attend more driving events to even out the wear Or you can have the alignment changed to remove the negative camber.
When I last aligned it, I set to 0 toe in the front, time passed, and the toe changed (to a fairly healthy bit of toe out). I hadn't been driving the car hard, so I didn't notice. The camber had hardly moved, so I didn't bother fixing it - didn't bother checking caster.
You get this when the bushings up front wear out. The reason I didn't fix the camber/caster move is because I'm dropping in some poly bushings soon, and the hardbar camber plates, and didn't want to duplicate effort.
If I was going to continue to run stock bushings, I'd be checking the toe probably monthly so I'm aware of the bushings wear and can fix the alignment before it starts eating tires.