Last scan date as old as 12/25/16

i have been noticing more and more that a large group of our servers with the version 14 client are showing a last scan date voer a week old.  we have daily active scans that do essentially a quickscan and a weekly scan that does a full scan. the reason these are showing an outdated last scan date is because they are still running a scan.  what can i look at to determind why the client still feels it needs to be running a scan.

thanks

Ian