This isn't exactly what you asked, but the Combined Presence community app can take two forms of presence and compare them to get a single output. It works quite well, and it has timeouts, logic, and everything built in. I use GPS, WiFi, and Smartthings presence sensors to get a picture of who is home.
The basic logic I use is if ALL of one person's sensors leave, they are AWAY. If ANY of the sensors are present, they are HOME. You can do ANY or ALL for away or arrived.
You could take this combined output and send notifications if you want to. If you are just looking to see if they are different and you are manually fixing the incorrect presence, this might help automate that for you so you don't have to manually reset things.
