Even Calor may not have a set regime for inspection as how can they? A consumer could have a bottle for 3 - 4 years before refilling it. Do they inspect every bottle regardless of how long it has been out which could vary from weeks to years?
We have an empty Calorlite bottle in the garage and that has been in the garage for a couple of years. I guess there are many Calor bottle out there that are well past their inspection date.
Because Calor do their own filling of bottles they have they check every bottle when its returned for a refill. A check is not the same as full inspection.
If a bottle is passed its inspection date it is taken out of circulation and either sent for full inspection or scraping.
If a bottle is in date, it is visually checked any signs of damage or misuse its taken out of service.
Providing a bottle is in date and appears to be sound, its refilled to its tare + charge weight.
That happens every time with a Calor cylinder so there is a very low risk that a faulty bottle would be reintroduced into circulation.
There will be old cylinders in circulation that have not been returned for a refill, but they are old becasue they have not been used very much, and that also means they are not very likely to have worn out valves so the risk is still very low.