Last contacted vs. Last status report

Can anyone explain to me the difference between the "Last contacted" and
"Last status report" date/time-stamps on computers in WSUS? What activity
causes each timestamp to be updated?

From observation, it seems a status report is when WSUS information gets
updated with which updates have been installed. When do computers report
this information to the WSUS server? It does NOT seem to be an immediate
thing. I have observed computers that have installed approved updates, but
the WSUS interface does not show that computer as having those updates
installed yet. If a computer is shutdown before reporting status, even the
next time it is turned on, it does not seem to immediately report status to
the WSUS server. Why the delay in reporting status? Is there any pattern to
the delay, or is it purely a random thing?

 

Yes.

"Last contacted" refers to any time the client contacts the WSUS server: for
initial registration, to selfupdate, to detect, to download content.

"Last status report" refers specifcially to the execution of calls to the
ReportingWebService, and generally occurs 15-20 minutes after the completion
of a detection interval.