Half of them are faces he’s never seen before and—he assumes—half are faces he’s seen (possibly often) but doesn’t recall. The experience is not new. He’s careful to advise those that he knows he’s meeting for the first time about his potential amnesia so as to avoid their likely diagnosis of early-onset dementia.
In truth, however, dementia shouldn’t be totally ruled out quite yet. He’s already blurred the divider between fact and fantasy so many times, either by accident or by deliberate, intentional, and repeated fictionalizing, that even his attempts to separate the two frequently fail.
The resultant vaguery has its benefits, though: much as he has come to recognize and even accept (and occasionally even boast of) his shortcomings, so too have most others he’s met and thus—mercifully—lowered their expectations of him.