Series can be a pain

,
What you describe as a boxed set, others call 'Omnibus editions': contains only 1) One series. I use the system first . last (always 2 digits)
2) Then there is the (complete) spinoff series: where a character goes on alone
series.spinoff and I don't include the books of the parent in the numbering
3) Then there is the interwoven spinoff

where the books intertwine
4) Then there is the 'Boxed Set' or Anthology that contains assorted (series) material that may only have a Common Theme
5) Then the Nightmare: Visiting characters. Where authors allow their characters to play in the neighbors Universe :jump in hole, pull rock over: so these volume belong to BOTH
6) And the one that is becoming more of a pain (because of the age span of the books

). Reused Series NAME. Unrelated Series with the same (downloaded metadata) name. I have 1 with 3 members, a bunch with 2 members: I need to catch these and break the name tie
7) Inconsistent metadata: The Series, Series. Or a Name change for the same series (Yes, Publishers do this

to us as well. The 'Books' list in the book does not match the 'Series List' at the Publishers )
Couple in poor device 'bookshelf' support. Items 2 thru 5 pose big difficulties.
Filename limits, Screen Display word count limits...
#1 seems to work on a simple file-folder system (My Astak) and on the K4 using the Plugboard
#2, 3 and 5 might be
solved by using a custom series-like column.
#4 (no direct hope). Use EPUBSplit and 'Un-box' the set
#7


'Constant Vigilance' to catch and assign to a unique Name
Read the various threads on what folk have tried and see if any fit YOUR situation-device