Before Egerton

Here is NRSV, Mark 7 -

5 So the Pharisees and the scribes asked him, “Why do your disciples not live[d] according to the tradition of the elders, but eat with defiled hands?” 6 He said to them, “Isaiah prophesied rightly about you hypocrites, as it is written [Isaiah 29:13],
 ‘This people honors me with their lips,
   but their hearts are far from me;
 7 in vain do they worship me,
   teaching human precepts as doctrines.’

8 You abandon the commandment of God and hold to human tradition.”

This is in the so-called Bethsaida Section, Mark 6:53-8:21. It is famed for being (1) redundant and (2) reproduced in Matthew but not in Luke. (Luke also doesn't quote 6:45-52 or 8:22-6 which surround it, but waaay back in 1998 I mooted that Luke knew at least these or some form of these.) Mark 6:53-8:21 is also thought to be primitive since Jesus does some magical weirdness in here.

As I read Egerton's minutes about the King's Coin, I see that Jesus there too quotes the full Isaiah pericope. Jesus is irritated that the <lawyers> are flattering him with their lips as working wonders above the prophets - meaning Elijah and Elisha, given that he's about to heal a leper. But how about those precepts?

Original Mark or else a later Marcan editor, by contrast, quotes Isaiah's comment about human precepts in context of an actual Jewish Rabbinic precept.

I propose that this anecdote belongs to an ancient Christian catechesis, which the Apostles attributed to Jesus Himself. Egerton transposed the quote into his Royal Coin controversy - falsely. Mark or his editor restored it.