Thank for the reply.
Apt only knows what it is told about distributions/sources through their Release file. My Release file for unstable/main has:Archive: unstable Component: main Origin: Debian Label: Debian Architecture: i386so those are the only distinguishing factors that I can use to differentiate that source. You can see what all your Release files say by looking through the files /var/lib/apt/lists/*Release .
Is there any kind od oddity here as stable/testing/unstable are rather temporary synomynous ? Thanks, Jerome