Some drives report PI and PO, other report PI and PIF (a parity inner Failure would normally result in a PO)
Like C1 -> C2 -> CU progression in CD error scanning, there is a similar progression of
PI -> PIF or PO -> POF
What the specifications say, and what works in practice, are often two different things - the main problem being that if it's riding close to the limit of non-fatal errors, any increase can tip it over into fatal errors.
So to be completely non-commital, it's a bad sign, just like skyhigh PI rates.