Interesting question, I served a 5 year apprentiship as a mechanic, attending college two days and three evenings a week, the rest of the week was at work. Sat the C and G exam in 72 and passed.
I joined REME in 72 and they said that the Army did not recognise the C and G qualification and thus if I wanted to be a VM would have to do the training at Bordon. Feck that said I and became a Clerk in REME.
Now if the Army did not recognise the C and G full certificate in 72 I wonder if the institute recognised the Army qualification?
Also for the C and G certificate I feel you would need to have passed the VM class 1 course.
Get them to do a search, I did this a few years back and they sent me a copy of my certificate. It appears all their records are held on servers in Germany nowadays, at least that is where my Copy Certificate was posted from.