Correcting Hitchens' Razor to Hitchens's Razor

In an earlier post, I suggested the take up of "Hitchens' Razor: That which can be asserted without evidence can be dismissed without evidence."

On reflection and several comments on Why Evolution Is True, I have compelled myself to get it right. This is important for a Gnu Scientismist, as Pedantism* is one of the Preferred Virtues.

According to the Apostrophe Protection Society and my Vietnamese-born wife, the correct use would be "Hitchens's" due to the possession being singular. If there were multiple Hitchenses that owned the phrase, it would be "Hitchens'" but we all know there was only one Christopher Hitchens.   I do recall from English classes that if the word ended in an "s" the apostrophe had to follow it, but that may be either mis-remembering, or bad teaching.  It appears I only know grammar with bad practice, and not in theory.

So, it is somewhat fitting that I need to correct the record and make this a teachable moment, because:
a) Everyone should get into the practice of unashamedly realising, admitting and correcting mistakes;
b) Christopher Hitchens would have appreciated being a teachable moment for the correct use of the apostrophe; and
c) Pedantism, as a virtue, can be fun.

* Ie: Being pedantic - pedantism is not a word :)