Baen call those Omnibus editions
Where 1 to 3 books in a series have been combined into a single volume.
I currently use an Omnibus tag, but that does not easily cross reference to the individual (original) titles, using the Omnibus title as a reference link only.
I am looking for ideas
Condition 1: Individual books are in library, and series indexed in order <Calibre does this well
Condition 2: Omnibus is in the library, no individual book index overlap < 1) How to make cross a reference entry 2)What to set the series index value to for the Omnibus
Condition 3: A mix within a series of Omnibus and individual books < series index setting a huge issue
I already use empty books
as (and tagged) placeholder for future release/purchase markers
Next up: Author Pseudonym cross referencing within Calibre