Kings Ferry's original scheme was rather quirky in itsself, by use of its decimal point. That was lost with the "first" renumbering to fit NatEx's computer system some years ago. With some notable exceptions (such as the very first Caetanos being numbered in the 6-series to differentiate them from the motley collection remaining in the 4-series, and VIP coaches becoming 9-series), the first digit always used to specify seating capacity. Fleetnumbers have also got substantially smaller in recent years, declining in size from the inch-high numbers next to the door to tiny numbers barely visible somewhere on or around the front. Even the new numbers appear to come in two different sizes!
Further examples fished out of flickr:
BU18 YTR appears to be 53118, but very hard to read.
BF68 ZFE - 5730
BF68 ZFN - 53126?
BV69 LNK - 5734
EK06 - BX65 WCC - 4830
YG68 TKF - 3415 (although when photographed was still showing old fleetnumber, so 3415/302!)
Chris