Does anybody know what this means?

I have sent PMs to several parties and requested a conformation that they were recieved. When I first login it simply says I have no unread PMs however when I click on something else it lists all of my unconfirmed messages. Is it possible my messages were read but never "confirmed" that they were read? I appreciate any feed back. Thanks.

dont know if it does it here but ive had messages that i have read and got a message if i wanted to let the sender know that i read it / i just put no