Engineer qualifications, such as the British CEng or the American Professional Engineers' Licence have a de-facto sliding scale. Being simplistic, to get your licence you have to hit a point on a sliding scale.
At one end of the scale is a great deal of experience and only limited formal training, whilst at the other end is a great deal of formal training allowing rather less (but still significant) professional experience. And in both cases, you need recommendations from several already-qualified practitioners.
There is much debate to have concerning the detail of such a system, but if one were looking to create a universal TP/FTE licence, this is probably the sort of model that you want to go for.
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