Chevvron
You raise a good and interesting point.
I have wondered what ongoing training of ATCOs takes place - if any.
I do recognise the problem. If ongoing "training" was a requirement then inevitably some one must pay and I assume ATCOs are neither well paid and if their employers met these additional costs it would be yet another expense for hard pressed small airfields.
That said perhaps the CAA should take responsibility for "vetting" ATCOs say once a year without charge as part of their responsibility to ensure standards are maintained.
It does seem to be the way that whenever someone is excercising a professional skill that impacts on others some form of vetting is de rigueur.