As an example of the complexity in finding out your sodales, look at this: Sulpice could not know, whether eventual sodales had their Parmae up. He could only scry on them with his 5th ring (RoP:TD p.100), which has no real casting roll and no provision for forceless casting. So he asked a shibboleth-type question and was promptly misled by Yannis, who knew the Oath of Hermes without having taken it.