blinky-
In general that’s how Dor Yeshorim works, but anyone can go to their local lab, have the tests done and the results given to them.
Of course if two people are told that they are not compatible then they know that they are both carriers. They are supposed to keep it a secret but you know what ends up happening.
“Well you have to promise not to tell anyone because I did and so did the person who told me…”