Software uninstallation (Software Asset Management)

We are using an in-house product to install software on laptops/desktops. The same data is used to populate 'Software Installation' table in ServiceNow.

Now coming to software uninstallation, end users themselves uninstall the software whenever they want or the desktop agents will uninstall based on a request.

The in-house product does not have uninstall capability and it cannot track uninstalled products.

In this case, what is the best way to calculate reconciliation (because now all the entries are there in the Software installation table, and some software is uninstalled)