OEM 13.3 usage of named credentials

I'm using OEM (version 13.3) for a while now, but this one thing is still unclear;

If you manage databases, you are being asked to login. Alright. In OEM this is done though "Credentials". The regular type of credentials are "named credentials"

Now, I pick any database, and I'd like to review some details. He's asking to choose the correct credentials, to login. Now comes the problem : I have tens and tens of credentials, a lot of them suited for any database, and at least one of them suited for this specific database.

But, instead, the scroll-down list of named credentials is showing two of them. They are intended to be used for other databases. Stated differently: the correct one isn't there.