In the "real" world - a fabled place that I've heard rumours of, somewhere beyond the vitamin D deficient world of dead languages, libraries and computer screens - oral language is the superset and written language is the subset.
Point 1: What I've noticed about people moving from a written knowledge of English to a spoken knowledge is that the spoken language is seen as, and for all intents and purposes becomes a subset if the written.
Point 2: The written language tends to absorb and transmit forms long after they have left the spoken language. So the written language doesn't really represent the "true" spoken language of any particular era.
How could these two problems be tackled with regard to post Greek education, pre-/in-service training of Greek Language instructors?
Specifically, how could the sub-/super-set imbalance be rectified?
"If you can't explain it to a six year old, you don't understand it yourself."
(Attrib. to Albert Einstein)