A life raft is the one piece of safety gear nobody sees working until the day it has to. It lives sealed in a canister or valise, and the only evidence it'll inflate is the service label. That's what a surveyor reads.
Intervals
Practical Sailor sets out the rules. In the US there's no inspection requirement for life rafts on recreational boats; the maker's guidance applies. In Europe, ISO 9650-1 allows up to three years between services, but makers often specify shorter intervals, and some rafts need an annual service after their first three years. Charter boats can face stricter local rules: one owner on the YBW forum reports annual recertification for a Greek charter boat.
How a surveyor checks it
Read the label on the canister or valise: the last service date, the next due date, the capacity and the maker. Ask for the service certificate. Then the stowage. Can the raft be launched by one person in a seaway, is it secured so it won't go over the side on its own, and is the painter made fast to a strong point. If it sits in a cradle with a hydrostatic release, check the release's own expiry date.
The finding depends on the use. A raft a year overdue on a coastal boat is a B. The same raft years overdue on a boat about to cross an ocean is an A, because nobody can say it'll inflate.