Notice also, in Graham's link, that when you have to renew your licence at 70 (as everyone does) there are medical requirements if you want to keep C1. This seems to apply regardless of whether you obtained your C1 through a separate test or by "grandfather rights" from pre-1997.
Even a pre-1997 driver might find that the C1 (and D1 minibus too) has mysteriously vanished from their licence, if they've sent it for replacement at some time. I'm told DVLA have got their act together a bit now, but there was a long period when licences were coming back with only post-1997 classes. DVLA would say there was no record of what was on the old licences as they were routinely destroyed. During that period, the only sure way to keep your C1/D1 when your licence went away (even for a change of address!) was to keep a photocopy as backup AND enclose a letter pointing out the categories on the licence.
Personally, I'd still be inclined to take those precautions even now - perhaps I've heard public bodies say "it's OK, we've sorted it now" too many times! (Cynical? Moi?)
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