[throwaway9385]

> How many people, a couple of generations on, would remember the precise dates

The people who witnessed Pompeii in person probably remembers it pretty well. This is why I trust his recollection, even if Pliny wrote it down decades later.

It's also not unreasonable to assume he talked about it several times between the event and when it was written down, so that it was easy to remember the details.

[eszed]

That was my point, too, though I can see how that was unclear.