We know about part of the problem:
There was an initiative to make the outdated HCPCS concepts standard. But it's still not fully implemented,
select * from concept where vocabulary_id= 'HCPCS' and invalid_reason ='D'
and concept_code not like 'D%'--CDT codes - so it's wrong
and concept_class_id != 'HCPCS Class' -- these are deprecated as it's a wrong classification
and domain_id !='Drug' -- non-standard anyway, are mapped to RxNorm or RxNorm Extension
So all these concepts should be standard (mapped to itself).
And if you find something else it would be really interesting, so yes, please share