Most benefits are public, which provides incentives for people to attain a higher elite level. As you suggest, there are benefits which are not public. These fall into two categories: official non-published benefits are based on internal airline policy, available to customer-facing employees in the relevant work areas (such as reservations, flight attendants, etc.) Unofficial benefits are casual benefits extended by an individual airline employee, as a matter of custom or as a favor, but are not based on airline policy.
Airlines may establish official unpublished policies in an effort to simultaneously (a) retain high-value passengers who might otherwise defect, and (b) keep the benefit quiet to avoid having large numbers of people request it, or to retain the flexibility of changing the policy quietly, or simply to keep the published benefits simpler.
Individual airline employees may extend unofficial benefits out of a sense of fairness or in an effort to keep high-value customers happy.
It's difficult to get into details without being limited to a specific airline program, but examples of official non-published benefits include:
- Free food and/or drinks when otherwise not entitled (such as flying
in domestic coach or in a domestic airline lounge).
- "Hidden" award
inventory (award seats only available to members at a high or top
- Ability to use system-wide upgrade instruments for
flights later than the expiration date
- Earning additional system-wide
upgrade instruments or redeemable frequent-flyer miles for travel
beyond a threshold
- Making desired inventory available on special
request (such as opening an award seat or a discount fare bucket)
Examples of unofficial benefits include:
- Upgrades on non-upgradeable tickets (e.g., an award ticket in certain programs, discount inventory in certain programs)
- "Protection" during irregular operations (being booked into alternate flights as a backup while still holding confirmed space on original flights when the original flights are delayed)
- Being admitted into a lounge not permitted by status or class of service (e.g., a first-class lounge when flying domestic coach)
- Changing flights without fee (when a fee would normally apply)
- Receiving a larger number of bonus miles as an apology when something went wrong