In signing the September Statement one commits to declining "to volunteer his or her individual services to the Philosophical Gourmet Report while it is under the control of Brian Leiter." In signing one is not suggesting that one had been asked to serve or was likely to be asked to serve the PGR.
In signing the October Statement one announces one's support for "No rankings, not now, not ever."
As far as I can see, one could sign both statements with full consistency.
Richard Heck agrees that one can sign both statements with full consistency. http://rgheck.blogspot.com/2014/10/can-you-sign-september-statement-if-you.html?spref=fb