Olicence renewal query

Anyone know why on one licence the vehicle discs say exp 28.2.17 and the paper licence says review date 16.3 .17 and on another olicence the vehicle discs say 31.12.16 and the paper says 31.1.17 ,why the differences ?

Payment for O Licence continuations must be paid before the last day of the month previous to expiry of the licence, which is the day when your discs run out.