Thanks for pointing this. Presently only CY8C28x45 and CY8C28x43 are mentioned in the RefMux datasheet(http://www.cypress.com/?docID=40299). RefMux uses Continous time analog block of regular analog column type. So all CY8C28xxx devices would not support RefMux, but CY8C28x23 and CY8C28x33 would support it apart from those presently mentioned in RefMux datasheet. Ordering info of CY8C28xxx datasheet (page 74 in http://www.cypress.com/?docID=46091) shows the devices that have regular analog blocks.
We have requested our doc team for the update of the RefMux datasheet with above changes in the next revision.
Thanks & Regards,
Your always welcome !