I'm not sure if that has been discussed elsewhere - at least I couldn't find anything. Regarding the series numbers, sometimes authors issue novellas as part of a series, but it's not part of their "official" numbering order. Would it be possible to add those novellas as a .5 (for example) between whole numbers to fit that novella in the proper sequence of books? For example, I just bought a novella that is a prequel to a series, and it could be .5 in series order.
I feel kind of bad asking for even more from you at Calibre, since it's my favorite program ever, but I'm thinking it wouldn't be a tough fix? And hopefully not a nuisance to those who wouldn't want it! Thanks for considering it, anyway.