be it ori or ap set they will hav sirim number unless u direct import in ur phone. so wat if u hav a sirim number how u proof it is authentic ? sticker can be made and bought.. imei no. for ap set will normally match the 1 on the sticker on ur phone under ur battery but it wont necessary match the one on the box. y is it important to check imei no. and match them to the sticker behind? maybe becos to giv ur self a believe tat ur set is not a recondition set lor.. ori set will always hav the imei no. same as the sticker on the phone and the box. the sticker tat cover ur screws/nuts on ur phone is jus to prevent u to open it up .. the number of sticker to cover those nuts/screw depend on the company.. sometimes even ap company hav all those nut cover with sticker.. so not so good to judge it as ori or ap..
so the best bet is get from ori reseller (save u the hassle when u r claiming ur waranty and worry tat ur parts hav been change with grade aa or fake part on the ap set)