Pretty sure it's been since day one. They have only changed how the attacks appeared in your rivals list.
been a really long time. I vaguely seem to remember it not counting but it changed before the pk death stopped you from attacking.
I thought you could still attack someone after you PK them. Only an AK or listing closed the retaliation window?
i guess im so used to collecting one hit kills that i have not every gotten that many attacks on someone when they have been on the list, but with so many people riding these days it is coming more commonplace to get in multiple attacks while they are on the list.