I have no idea what your exact point it. As noted by others, four players have beaten both Venus and Serena in the same tournament.
And what, exactly, makes that so special?
Williams fans are always talking about how the sisters should be treated as separate individuals, not lumped together as a group.
We are talking here about singles tennis, not doubles tennis. So a player's record against the sisters should be their record of playing them as individuals, not as a team.
Because, if they're working as a team in singles tennis, something is wrong.
I pointed out some years ago that Hingis and Davenport, back when they were numbers one and two in the world, could have pulled a Williams sister act and simply not played each other except in the grand slams.
But they didn't do that. One year, 2000, they faced each other in five finals, all of them big tournaments, (AO, Indian Wells, Miami, Zurich, Philadelphia.) But had they chosen to use a strategy of not meeting outside the slams, they both probably could have pulled very far ahead in the points race.
That's still my big knock against the Williams sisters, although I am no longer much concerned about them facing each other, because rarely do their meetings produce really good tennis, as the latest Wimbledon encountered once again proved.