My mother's maiden name is Comisky, and her great grandfather was Hugh Comisky. Not sure if it's the same person (he married Kitty Daly in San Francisco around 1910). Anyhow, when she visited County Monaghan a few years ago, a historian there told her that there are dozens of spellings for the name, both in County Monaghan and abroad. Part of the reason, he told her, was that postmen used different spellings to differentiate between different households before they had street addresses. So, for instance, if there were two Hugh Comiskys living in Broomfield, one would change the spelling to Comiskey (or Cumiskey, or Commisky, etc.) to ensure they'd each get their mail.