[sno]

What are the letters next to some of the descriptions such as the RBB codes?

They are catcodes (catalog-codes). The jeep guys love to refer to their rigs by the catcode (ie, XJ, CJ, YJ etc)
Here is the full list of all Isuzu catcodes:

CATCODE CATNAME YRRANGE
AS Acsender 03 -
TC Amigo 89 - 94
UA Amigo / Rodeo Sport 98 -
UP Axiom 02 -
TH Hombre 96 -
PF I-Mark 81 - 85
JT I-Mark 85 - 89
RJ Impulse 83 - 85
JR Impulse 85 - 89
JI Impulse 90 - 92
DI Oasis 96 -
KA Pickup 81 - 86
KB Pickup 87
TF Pickup 88 - 95
UC Rodeo 91 - 97
UE Rodeo 98 -
JS Stylus 91 - 93
UB Trooper 84 - 86
KT Trooper 86.5 - 91
UX Trooper 92 - 97
UY Trooper 98 -
VX VehiCROSS 99 -