It's that I compare my 2 plus years of avast usage with my similar timespan usage of McAfee before avast. In that same similar timespan of McAfee use, I did encounter
several Alerts of Viruses, Trojans, Etc. Heck, after some of those encounters, I would even end up performing Windows Reinstalls because it would turn out that the alleged Virus / Trojan couldn't be cleaned, quarantined or deleted.
Of course, back then, in the early 2000's, I didn't know about False Positives. I just took McAfee at its word. If McAfee alerted me that it had encountered a Virus / Trojan ... no matter whether it managed to block it, clean it, delete it ... or NOT be able to get rid of it, I just ASSUMED it was the real deal.
But, NOW ... in my wiser years
I know about False Positives and that an Alert does NOT mean you have encountered a 100% genuine, without a shadow of a doubt Virus. So, there's obviously no way of telling how many, IF ANY of those McAfee Virus / Trojan Buffet Alert entrees back then were genuine.