GC5YG 1933 Scotland

Why did some stations from this time period in Scotland sign "GC" prefix and others just "G"?

Prior to January 1929, all British amateurs had to have a special license for working stations located outside the UK. Those with the straightforward UK experimental licenses were issued with calls that had no prefix, those with the special licenses were all issued with call signs that had a "G" prefix if they were in England or Wales, "GC" if they were in Scotland, "GI" if they were in Northern Ireland and "GW" if they were in Eire. " So GC was Scotland; but not seen any others with GC prefix. Back of my card just has GC5YG printed at the bottom, with the " C" crossed out, and signed G5YG. A 1933 card, so would explain the "C" being crossed out.
Maybe the GC was just used for a short time, or not used at all by some ?
The GC for Channel Islands perhaps just post-war ?

G4UZN Info & Collection