Organizers for the Beatles would have probably had little problem finding local musicians familiar with their work. For decades, Chuck Berry counted on the fact that there were always local bands that knew his repertoire well enough that no rehearsal at all was required.
That’s just wrong. If there is any kind of criminal code for music then this would have put someone in jail.
Also, stage monitors weren’t in use until they had already stopped touring. The Stones tried to convince to go back on stage because you could hear yourself now, but they were already done with that scene.