These Boieng codes all become a bit of an irrelevance after a couple of refits and resales. EG a Boeing 757-236 is built for BA, gets sold to DHL. becomes a 757-236F (or 236SF or whatever). yet what still identifies it as a '36'? Very little I guess. I assume some of 'it' is in the electronics etc. Take 777's - all BA ones 777-236, yet they have 2 different types of engine! Some 757-236 never even entered BA service and went straight to Air Europe, and gawd knows where from then on....... BA 757-236 have 2 different engines aswell, so there's very little 'unique' about Boeing codes.....
Airlines 'tend' to keep the same number, e.g. BA has had 707-436/737-236 & 436/747-136/236/436/757-236/767-336/777-236.
If the plane was originally ordered by Cathay, it would be a 747-467 (or 777-367 etc).
The aeroplane keeps its original code, so you end up with Virgin and Air Atlanta flying 747-267s. Just as Virgin has (leans over and gets spotters book) 747-443 (originally ordered by Alitalia) or 747-4Q8 (ILFC) or 747-219 (Air NZ) or 747-212 (Singapore Airlines).
Codes can be numeric, alpha-numeric or alpha-alpha.
Confused?
WT