Practically speaking, the reservoir testing is up to you. Consider this: If yours is fifteen years old, and you are the only person who knows that, "you are on your own". The birthdates, thus expiration dates on CF-bound aluminum tanks and reservoirs are a DOT thing for certified fillers to heed. If a DOT-certified filler never sees your reservoir, it is up to your personal judgement. If it makes you feel unsafe to use your reservoir past five years, by all means have it hydrotested. This regulation is still on the books because the Feds do not have what they deem sufficient history on CF technology to persuade them to allow the same "life" as steel tanks.