Glass's gives codes in UK as R1180 for 6-850 (renamed 6L Oct 75) and R1181 for 6-1100 (renamed 6TL Oct 75); the codes are more about the engines than trim detail. X17 may be wrong but had the advantage of including South American build cars as well - so we need their codes (which may or may not be same as French build). Was it Weasel1984 who is our Renault code expert?? I think he's trying to convert lots of 70s/80s models (12/15/16/17 etc) from X to R series, but X was easy because it covered the range but R is specific to each version.