I'm not too convinced that the name would be corrupted to such an extent. Cordner and Cordwainer seem different enough to be free from confusion. I have a feeling, though no proof, that corner has it's own seperate origins. When researched in those surname history books you get in local libraries you end up with a different explanation every time, if the name is in them at all. I remember one that suggested Corner was Anglo-French for Cornet player or a worker in horn.