Unadvertised (adjective)

1. Not having been made known or promoted through advertising.
2. Not made publicly known.

Origin:

Un- + advertised.

Examples:

1. The store had unadvertised sales on certain items.
2. The position was filled by an internal candidate, and was never unadvertised.
3. An unadvertised event takes place without any public announcement.
4. The unadvertised job opening was filled before it could be published.
5. The unadvertised sale was a surprise for the customers.