Outside Alexander Dennis this morning was Stagecoach E300 SN64OJC.
It had disappeared when passing tonight.

A post by "gka472l" on the Merseyside Dennis Dart Forum confirms SN64OHZ as 27151 and links to a photo of this.

Assuming they are numbered in order, this gives the following:

27143  SN64OHR
27144  SN64OHS
27145  SN64OHT
27146  SN64OHU
27147  SN64OHV
27148  SN64OHW
27149  SN64OHX
27150  SN64OHY
27151  SN64OHZ
27152  SN64OJA

2715?  SN64OJC

As i was away on my usual jaunt to Teeside at the weekend i don't know if i missed "OJB" or if it is the first "missing" registration in the sequence.