Thanks to an upgrade to the book cover software I currently (no longer) use and the latest Mac system upgrade, the book cover updates I attempted to did not want to update. The move from Book Cover Pro to Acrobat Pro to Acrobat Distiller went down the tubes.
So far as I can determine, once the document entered the realm of Acrobat, various dimensional details failed to translate properly. I'm not all that surprised as the last update of Book Cover Pro for Mac 10.7 took months to come through and even then, it was buggy.
So I rolled both The Mechanic's Companion and The Art And Craft Of Cabinet-Making back to their original covers for the time being. I've ordered up a copy of Adobe InDesign CS6 and will use that for all future content and covers. In other words, I have bowed to the ten tonne gorilla and give in to Adobe.
Till next, Gary