Probably the first batch of inlays made after the other chips and someone forgot to clean the roller/drum. In normal printing a few sheets are normally fed through to 'clean' any left over impression. This is what often constitutes printers waste.

Either:
No-one noticed and they went ahead and used them
or
PS couldnt care less as they were home poker chips
or
Someone deliberately used the waste inlays

It would never normally be allowed if it were a 'real' chip.

That said, quality control doesnt pick everything up and these things happen. Previous threads on similar topics have shown that many condsider printers waste items to 'detract from appearance' and are therefore worth less. This is why such 'errors' are not shown in TCR.