If it was New, I would say that setters should reject this in the future as it isn't accurate. But as Yourself and Prof M have stated, It's been doing the rounds for many years. So if it has become a standard, Then who am I to disagree :-)
I hear you NAC, But 'It' and 'SA' are valid in the Dictionary. Whereas 'EC' in the Dictionary is '(in London postal code) East Central ' Which is a district (Not a City)
Maybe i'm just becoming a pedant. But I believe that at this level of setting, Things should be correct annotation.
I trolled the internet and the big book to find a good/valid reason for 'EC' Only to find that there wasn't one. That to me is unfair to the solver.
But at least I will know better for the next time it raises its ugly head. :-)
Pedant or not, Klazo, you are quite right - but I think that answer is so embedded in the world of crosswords, we will never be able to eradicate it. It's actually very unfair to new solvers, they'd be unable to justify the equivalence!