They seem to be titles, as many of them have given us different names for purposes of the Jaunts they appeared in. ROSE was the Magician, SAGE was the Hermit, PSYCHENet was the Lovers... The Fool only took the name Don Orlea when I gave him mine on accident.

It seems to happen once every few months. Sometimes it is sooner than that, but it has never been shorter than four weeks in between arrivals... at least, if my calculations are correct.