OK, I know now I'll have to look up the reference I'm thinking of...
It related to the piece of brood comb that is kept securely and, once a year, cultured to confirm the AFB spores are still able to germinate (?) and propagate.
It was, I think, a New York state bee inspector who had taken the sample as part of a court case against some beekeeper. And (I think it went) after the legal stuff was over, they just kept it - and that is the story of why/how we can say that AFB spores can survive for so long.
*Somewhere* I read the story, maybe written from the point of view of someone who had worked in the lab? It isn't in my own archives, so I'll have to go further a field to re-find it...