Yeah, it's confusing, but Last Tried is just as important for my reporting as Last Seen... *especially with Active Scanning.
Active Scanning attempts to scan anything that authenticates to a domain controller - regardless of if it is a windows machine or not. Example, if you have ESX hosts that are joined to AD, it will scan those with active scanning too...
So for me, I have a lot of VDI machines that can't get scanned due to a few reasons, however, LS attempts to scan them because they authenticated to a domain controller. The result is a blank 'WIndows' asset in red, OS is 'Not Scanned', etc... but the Last Tried value keeps increasing daily.
It's a great way for me to tell 'hey this box used to scan properly, but now it's not' or 'hey is this asset *really* inactive?
but yeah, confusing.