Typically, the second letter denoted a facelift to the range, and the first letter denoted a redesign.
Hence, you will find folk talking about VH, VJ, VK and CL Chargers. It is worth remembering that, again no matter whether it was Ford, Holden or Chrysler, the two letter code refers to the whole range whether it is a two door hardtops through to a ute.
As a quick guide to identifying Chargers:-
VH
Rectangular headlights and driving lights (if fitted)

and multi blocked tail lights

VJ
Round 7inch headlights, and painted surrounds to front indicators

and retained the mult block tail lights

VK
Round headlights, grille typically painted white/grey and chrome surround to front indicators

and redesigned tail-lights

CL
Complete front end redesign

but retained the VK tail lights

I hope that helps.
To the best of my knowledge, only VH and VJ Charger were exported to the U.K.