I've noticed this pattern with the chapters and volumes of Pokemon Special, namely that every three chapters so far roughly adds up to a total of fourteen volumes. So we have RGB-Y-GSC total fourteen volumes, RS-FrLg-E is also for volumes, and it's likely going to be about the same for the DP-Pt-HgSs chapters, too. These fourteen volumes fit the generation of games that the chapters take place, with the exception of RGB-Y-GSC which is spread over two generations, but are so close together compared to the other gens I'm happy to lump them as part of the same saga. I'm not saying it's deliberate, but it's an observation that I think could be useful for categorization purposes.
Re: PokeSpecial 'Generations'
HGSS ends next volume, so yes, it will be 14.