The converter will have suffered some caking on the honeycomb inside, which is normal with oil consumption.
However, with only 5k miles on a new converter and the problem pretty much cured odds are that most of what was caked in there has burnt off. It will never go away completely.
The only way of knowing for sure is by disassembling the converter, but I agree that if the car runs fine with no CEL you should not worry about it.
The great part is that the lowly PCV valve took care of the problem. The problem in this case was that the PCV was not completely frozen but was simply gunked up. This would explain the not sounding right part the mechanic referred to.
They should sound like a rock in a tin can but if they have a somewhat subdued or muffled sound this means the PCV is gunked up.