Thank you for your response. Sometimes I've checked contacts when they are "offline" and sometimes while they are "online". I have read a couple of your other responses on this subject, but am still a little unclear. When you said, "last seen' means the last time that your contact was seen online BY THIS SIGNED-IN CLIENT (the contact could easily have been online while this client was not even running, and it would be impossible for this client to know)"
'last activity' means the last time there was some kind of Skype activity (like a call or an exchange of chat messages) between your contact and THIS client (not this Skype name)
I am assuming by THIS SIGNED IN CLIENT you mean me on my own computer which Nobody else uses. If this is the case, there have been two recent times when I have been online and other contacts of mine have been online simultaneously; however, when I scroll over their icons (while online or not) it still gives the same dates and times from several months ago.
Thank you so much