The tenant identifier is a Cerner assigned identifier that represents the organization housing the data (hence, tenant). There are some Cerner clients that share logical space within an environment, thereby acting as tenants in a single physical database (though their data is logically separated). Each of these clients has their own tenant identifier.
The questions you are asking are very difficult to answer without getting into specific organizations/clients/customers/etc and seeing how we both identify these organizations. This is why this need has yet to be solved in SMART as part of the standard (and similarly, CDS Hooks). I've talked with app developers who bill at the Cerner tenant level (making the mapping an easy 1:1) but also talked to developers that bill at a more discrete facility/building level. Also, it is not just a billing discussion as many developers have the same questions you do but it is because they want to map the Cerner tenant to some proprietary data they hold.
-Kevin