There's no way I'll ever know for sure.
My wife was 37-38 years old when I met her.
She was fucking before she was 18, and was single for a fair portion of her 20's, so she dated lots of men.
If I assume she swallowed a load at least once a year, that's 20 right there. And some years, especially in her 30's, she blew a helluva lot of guys. Definitely more than one per year!
She gave excellent head, too! She was very skilled at it, and it was her 'special' thing she liked to do for guys.
And she preferred to swallow; in all the years I've known her, she's only taken one facial.