The carbon fibre bottles are different and do have a finite life as you say. In the real world however I'm not certain what this means as you don't actually take them in to a dive shop for filling so any rule could be ignored by the owner. The bigger carbon fibre tanks I understand have to be junked as most of us don't have our own compressors so we have to get them filled and tested.The real hazard is when you condsider how many rusty rifle tubes are out there on older rifles with no checks made on them whatsoever.