I found the system I was thinking of. It was in an old (early '90s) catalog/listing of Hobby Heaven, which I think is now known as Spotlight Hobbies. Dunno if this system is anything like "official" but it does provide something of a useful starting point, at any rate. Anyway, here is what they had in their catalog:
Promos are reated for overall condition, appearance and restorability on a scale of 1 to 10:
10: Like new
8: Excellent, shows very minor wear
6: Good, may need some restoration
2: Rough, major restoration or parts
They also had some helpful abbreviations/shorthand for damage:
C1: Chrome very slightly worn
C2: Chrome moderately worn
C3: Chrome badly worn
(No C rating means chrome is in good condition)
V1: Vent or windshield post slightly bent or cracked, repairable
V2: Vent or windshield post bent or broken, possibly repairable
V1: Vent or windshield post badly broken [Snake's note: or missing completely?]
R1: Very slight warpage
R2: Moderate warpage
R3: Badly warped
J1: Slight "smile"
J2: Moderate "smile"
J3: Bad "smile"
H: Hood ornament(s) broken or missing
WWP: Whitewalls painted
T: Taillight(s) missing
G: Glass crazed or "foggy"
I: Other imperfection(s)
Hope this is of interest/use/help to someone.