I think the date stamp only applies if you are going to take it to the track, not sure of the finer details but Im sure the other forumites can shed more light on this.
Regarding the crease, yeah its normal if you have a shaped butt
I wouldnt think the wearing is normal after a week, depends how old the seat is. I've had 2 in my mx for nearly 5 years now and have only wearing where you jump in and where the seat belt comes over, but they are really only a thin material by no means really hard wearing. But mine seem to be lasting well.