If you've confirmed that including a version number in the ZIP file name doesn't affect the URL, that's great! I haven't checked recently, so maybe it's no longer an issue.
The Addon Manager is not the only way to install OWAs as far as I know (I have not used it). What happens during development when the
npm script is used, or when the OWA Management interface is used, or when a manual install is done? My guess, although I could definitely be wrong, is that these other methods together are the more commonly used install mechanism.