I've just found this feature in the new 0.7.5 version, and am quite pleased with it. However, I'm not sure how to deal with numbering of both the main series and the sub-series (and the Honorverse books are the main culprits

); any advice?
Also, is there any nice way of dealing with books which may or may not have a sub-series when sending them to a device or saving them (rather than having to use yet another possible saving format)?