"It has been happening since professional Flying Licences were introduced,the problem does get mentioned in at least a few pilot autobios."
IIRC there was guy who flew for well over 10 years for SAS and reached Senior Captain and had no qualifications whatsoever - I suppose you could say he could clearly do the job.
It happens in all walks of life. Not that long ago a VERY senior person at a major financial company quietly "retired" - one of junior their junior auditors ran a check on some of the Board and found one had very few of the financial qualifications he claimed to have.