At the moment, while you can save multiple credentials for a given application, if one set of Credentials fails to connect, there will be no additional attempt to access the application using additional saved credentials! (bug?)

For example:

2 Database servers (same type), running on different Hosts, and each has its own set of native users.

Save 2 sets of credentials, one per server.

Discovery will be able to access both servers, but only one will return results for the DB pattern, while the other will fail due to wrong credentials. 

(Tested with MSSQL)

Workaround (e.g. for 3 MySQL servers, each with separate set of credentials):

1. Duplicate the same Application pattern - one instance per set of Credentials
2. Edit the Application name in each pattern: mysql1, mysql2, mysql3 (respectively)
3. Enable the new patterns
4. Add one new set of credentials per "application" respectively

For each server, 2 patterns will fail, and one succeed.