Discrepancies in device count, subscribed vs. total

I’ve noticed something odd over the years, but until now haven’t thought to pursue it, and now only because of licensing concerns.

Say for example, say my deployment shows 6,000 total devices in “Computers” in “All Content”. In “License Overview”, my subscription is set as “All Computers” for the sites in “Lifecycle Management”. However, my count for subscribed computers may only be 5,750. Comparing the lists, it looks like devices that haven’t reported in for awhile are being “dropped” from the subscription count.

I try to clean out devices I know don’t exist, but there are some inactive ones I know do exist and I leave them. Does Bigfix drop inactive devices from the subscriptions after a certain period of time?