To be best of my knowledge, Naim say this about Service intervals, on the Naim Audio website:
How often should I service my Naim product?
This is a question often asked, and the Service Department recommendations are as follows: for the Chrome bumper (circa 1975 to 1989) and Olive (circa 1989 - 2000) range products, we recommend every 8 - 10 years and for the newer Black products (2000 - present), every 12 - 15 years.
OK, That’s fine. But… how about an Olive unit which is serviced today, by Naim or an approved agent…? Does its Service interval remain at 8 to 10 years, even though present day parts are used…? Or is it now 12 to 15 years…?
I’m sure the intervals are equipment era specific. They’re not restoring olive to black performance, they’re restoring olive to olive factory spec. Like watches, cars, and now my list has run out I’m not sure if a part is obsolescent, and replaced with a modern alternative, happens all that often, or of it does but in limited cases, if that’s sufficient to uplift the service interval for the entire box.
I’m just guessing though, expert opinions are inbound I’m also sure
The intervals are in many cases just a guideline so I wouldn’t get too hung up about a couple of years one way or another. Use your ears too; if something still sounds great after 8 or 10 years then a service may not be so pressing. On the other hand, if you feel something is no longer getting the hairs on your arms to stand on end, or making you want to go on listening for longer when you listen to it then it may indicate that something is a bit off, in which case a service is probably a good idea.
For all that, as their components age the regulated power amps can start to go off colour after 8-10 years, and this can get worse quite quickly, so I would with these I would stick to the recommended service intervals quite rigidly, and if you feel attention is needed earlier then let your ears be the judge.