data from deleted sites still in wp_usermeta

I’m currently testing so I’ve been creating and deleting sites on my multisite network. In the database I noticed that some of the data from deleted sites is still stored in the wp_usermeta table (meta_key = wp_##_keyname).

Is this a known issue? Can I just delete this data without worry?

For example, site 13 was deleted. In the wp_usermeta table there is a meta_key of wp_13_user-settings.

Thanks for any help.