How can you tell which computers are authorized in iTunes? my account says I have 5 computers authorized (maximum allowed) but when I look at authorized devices it shows 2 computers and the rest are phones or iPads

How can you tell which computers are authorized for iTunes? Apple only allows 5 computers to be authorized but when I look at the authorized devices in my account it only shows 2 computers and the other devices are iphones, ipad and itouch. At the activation query it only allows you to select to deactivate all computers rather than just certain ones. I am sure I have some old computers that were never deactivated but if I deactivate all of them then I worry I will not be able to activate the current computers.