What should it look like when your SQL servers are properly licensed?
Aha, those will always be disabled and null, according to the SERVERPROPERTY (Transact-SQL) manual page:

LicenseType:

Unused. License information is not preserved or maintained by the SQL Server product. Always returns DISABLED.


NumLicenses:

Unused. License information is not preserved or maintained by the SQL Server product. Always returns NULL.



The query is not correct.
Instead, I need to download Microsoft's Assessment and Planning Toolkit (MAP).