This is what happens when people start messing around with the regs - the 16th edn had it cast in stone that using a green/yellow for anything else is a no! The same snippet from the 1992 (amd2 1997) regs I posted over in the plumbers forum:
Start adding words to it in the 17th edn and it causes confusion. So reading the 17th edn regs it would appear it is allowed but anyone trained in the 16th edn era would probably not condone the practice out of good workmanship.
Let me start by agreeing wholeheartedly with your belief that use of (oversleeved at ends) G/Y-insulated conductors is bad practice/workmanship - and just as much today as under previous editions of the regs.
However, since we're discussing 'the word' of the regs, I'm not sure that I agree with what you say above. The 17th ed. has certainly explicitly prohibited G/Y singles from being used for anything other than a protective conductor (in a way that the 16th ed. did not). However, as for other (multi-core) cables, both 16th and 17th eds say the same thing - and what they are prohibiting is the use of G/Y colours
for identification of anything other than a protective conductor. As for the meaning of 'for identication of', 514.3.2 of 17th ed (and, I suspect, a corresponding reg in the 16th ed.) requires that cores must be identified "'at their terminations and
preferably throughout their length".
Hence, assuming it contained something similar to 514.3.2, I think that the material you quote from the 16th ed
would probably have allowed a G/Y core to be used as a live conductor, provided it was appropriately identified (by over-sleeving) at its terminations - since to have that identification throughout the length of a cable was (and still is) only 'preferable', not mandatory.
...but, as above, none of that means that I regard it as a desirable practice!
Kind Regards, John
