The "Recent Comments" section on the right is all in upper-case, making all us clever comment-makers
LOOK LIKE SHOUTING IDIOTS. CAN YOU ADJUST THE
div class="block" id="block-recentcomments">
to give us mixed case again?

Some answers for karnuvap:

A recipient has one potential donor at most going through the process at a time. The process is pricy (typing plus medical suitability) & so insurance companies pay for only one at a time.

If a match is identified with a different recipient & the match the other way works as well, the operations are done simultaneously to reduce the chance that only one of the operations goes through (donors back out, donors or recipients become medically incapable of proceeding..).

The discussion at the link includes a link to another paper that computes 3-way exchanges. More then that is considered impractical because of the need for all the operations to occur during the same short period of time.

-Jim (I almost donated a kidney & learned a lot).