Not knowing the weight of AG jeans, I can only speak from experience with traditional Levis-type of denim. If they are snug, they do stretch out as you wear them, and since there is only heavy weave cotton, they don't snap back after wearing - unless you wash them (and definitely if they go in the dryer). Which means, if the knees bag out, they'll stay that way, unless washed. So, if they already have room to spare, they'll just get even roomier.
In ye olden days of 1970's, pre-Gloria Vanderbilt, we would put on our 501's (and you had to do the math to convert the standard men's sizing to female), sit in the bathtub, and then walk around in wet jeans for a few hours (turning indigo blue in the process).