When my Silvia was imported from Japan the Cat needed to be replaced for Australian Compliance. From what I can tell Australian Compliance means removing good Japanese stuff like the Cat and seatbelts etc. without an Australian compliance logo on it and replace it with the cheapest nasty stuff the car importer can source locally with a logo.
A couple of years later I was driving along and the car suddenly wouldn't rev past about 2,000rpm and had a funny almost a whistle from the exhaust. The cat has died and the material ended up in the rear muffler almost completely blocking it. I ended up with a whole new exhaust as I needed a new cat and new muffler and the pipes had been badly damaged from hitting something before I got the car.
So yes Cats don't last forever and cheap ones can wear out very quickly, best to replace it before it fills the muffler with rubbish and blocks it.
