I guess main thing is that phone is considered brand new in terms of warranty, so you should not need to worry about that, if phone does not have any visible failures.
However as I mentioned, batteries rarely get better in time, so extra shelf time definitely is something that is left for client to worry about later on, so it would be fair in my opinion to have some marking on the box telling about that. It would be best if all product with batteries had best before date marking on them (just like when you buy normal batteries there is always date markings telling that).
My main concerns with my current phone is that beside battery there are some cosmetic issues that may cause problems later. I know peeled off colour in steel rim is considered normal use but mine is also very slightly bent. I'm not sure what their manufacturing tolerance is for bending. I hope it is not going to cause problems eventually. Luckily bent is so slight it is hard to see naked eye (but can be verified by placing a ruler across the screen) and so far no issue with iPhone leather case fitment or non 3D tempered screen protector. I'm not sure if 3D screen protector would hold as well due to that problem since those are more rigid.