I'm also going to leave Y'Vanna out as she isn't from Guillan and hasn't been there long..  I'm sure that thief's cant is known everywhere but I'm almost certain that there would be some differentiation in different locales.  She is also not exactly a thief, well I mean she is, but it is somewhat of a new profession to her.  I am also very sure that Y'Vanna would like to learn, given the proper time and place.

     None the less, I think that is a fantastic idea..