The printing of Rambam's Mishneh Torah by Hotza'at Shabsi Frankel was a revolutionary achievement. The publishers searched the globe for the earliest and most authoritative manuscripts and attempted to achieve the most reliable version of the text. They also compiled what is called the Mafteach, a cross-referencing index of any mention of the Rambam, or it’s “Nosei Keilim”, in thousands of ancient and contemporary seforim.
Another alternative element of the printing of this set is the unusual breakdown of the volumes. The Mishneh Torah is comprised of fourteen books, and the Frankel Rambam reproduces it as such. However, instead of numbering the books 1-14 (or א through יד, in this case), they refer to Madda as א* and Ahava as א**. Then they continue a standard numbering sequence through ו, at which point we find Avoda as ז* followed by Korbanot as ז**. Thus, although there are fourteen volumes in the set, the numbering only reaches 12, יב. We are led to believe that Madda-Ahava and Avoda-Korbanot are somehow unified sections. (see the picture in the link above)
Why is the Frankel Rambam divided the way it is? Why did the publishers choose to number the volumes in this counter-intuitive fashion? Is there any grounds to suggest some innate connection between those volumes - and if so, why was it never done before?