Found this over at Xda
Where to find the batch number ?
" Look at the SD Card Slot you will find a little black tab much like the sim card tray so pull it out with a pair of tweezers or if you have long nails make use of it and you will find out the information you would find usually behind a battery cover and such, the IMEI number, other serial numbers and of course, the manufacturing date."
14w15 : slight gap at the top right ( less than a mm ) , Camera lens off centered , dead pixel
14w16 : Dead pixel ( 1 - 2 ) , Battery over heat , Camera lens off centered ( up in left position ) , A gap on the top right and on back on the top left just above the camera lens ,
14w17 : Overheat from using 4k video recording , 1mm gap on the top and bottom right corners and around 2mm gap on the bottom left corner. , flash is so far off centred that the complete top left corner ,
14w18 : A gap in the bottom left of the phone ( can easily fit a piece of paper or a pin in the gap). Also have the off center camera ,gets warm even when just using Chrome. , dust under screen / camera lens ,
14w19 : the camera is slightly off center ( doesnt affect the image quality ) , tiny gap at bottom left.
My phone is 14w19. The camera is certainly off-centre. I never noticed until this. Gap doesn't look as bad in the pics. It's not a big deal I think.