I've never heard of the stains coming out over time, especially since you don't need to wash jeans too aggressively unless you're sweating in them.
One of the keys with these types of pre-stained jeans is to ensure that everything lines up okay on you. Sometimes they're stained in such a way as to hit certain points of the body, e.g., around the knee or back of the knee (especially with fades), so if you're a lot shorter or taller it might look off. I suppose a splatter or more generalized staining effect would not have this issue.
There should be care instructions. In general, I have found turning them inside out and giving them a gentle "cold" wash with Woolite Dark is fine.