If I think I know what you are referring to, maybe I am not thinking the same, but all you have to do is click "reply" at the original post then it will be directed to the postee you want to reply to, it is easy to forget and just click reply at the last reply someone else has made. No need for rules of etiquette" as you mention, all we need to follow is to be nice, and no vulgarities when we post or reply, treat others the way you'd want them to treat you, that is the thing we try to keep here
Many people make that mistake of clicking "reply" after they read the last reply of someone else, most of us understand, it happens, if you want you can re-reply stating you made the reply to the wrong person, and then in the reply state the person you meant your reply to go to.
Take care now and enjoy the weekend

DE

In giving advice seek to help, not please your friend
SOLON