From what I remember, it's a metal stamp on the born date then 2 adhesive re test stickers then death?
Typically 15 year maximum life, with tests at the 5 year points for fibre wrap
It you miss a test then you aren't allowed to use it until tested.
You can test more often if required (e.g. You drop it and test to ensure it's not affected)
A late test cannot extend life beyond the final date
Standard aluminium can be used forever with no final date, provided they are in good visual condition and are tested when required. (Not necessarily financially viable to retest as they are cheap enough to buy) UKPSF information states 5 years, but there may be a 10 year allowance
There are other situations:
old ultra light bottles had short life and no testing, but off the top of my head i think any current model of ultra light is testable.
13ci aluminium is exempt from retesting, and can therefore be used forever whilst it's in good condition