Steven, Thanks so much for your response!

my head is still swimming slightly ;-) ... Sorry, as my girlfriend says, sometimes I think too much <g>

What I would propose as a 'counter-offer' is using a series tag 440 (or 490 - 830 if necessary), based on the understanding that these sets of books really are parts of series that are meant to be used in the way that you are doing. If you created/imported a simpler MARC record for each title, you could make the links with their hierarchical series by creating a useful local 440 (series tracing).

Yes, here's an example of how Oxford University does it with a 440: 440 0$a Oxford reading tree.$n Stage 1,$p Kipper stories In this case it *is* a *real* series - they are all books. How does Koha make use of this entry? Can the user just click and pull up a list of all the other books in that series? So if I have a CD-ROM designed to work with all the Stage 1 Reading Tree books (not just the Kipper stories), could I add: 440 0$a Oxford reading tree.$n Stage 1 to the CD's MARC record before importing into Koha, and Koha will do something meaningful with it? Note the CD-ROM would be an entirely different Itemtype, different shelving location, different call number series, etc.

Granted, this may not be a perfectly kosher use of the 440 -- what you choose might not be recognised anywhere else as a series --, but what you are proposing otherwise really would require detailed Analytics (library jargon) that would give any cataloguer a headache.

I'd love to learn more about "Analytics" - even though it is jargon (I've seen it in the MARC specifications), twenty minutes of browsing with Google didn't show much of use - any pointers to online Library Science tutorials?

In any case, what I am proposing would allow OPAC users the ability to find each individual title without necessarily making each individual record overwhelming (20-30 title- and/or author-title added entries plus the problem of deciding a legitimate 245 entry). Each record would have the 440 showing what group it belongs to as well as the call number which would show where it is

collocated/located on the shelves.

So 440 (mapped to an appropriate Koha field - any suggestions?) becomes a searchable field in the OPAC, returning all resources containing matching strings? That's (more than <g>) enough for now to inflict on everyone in the list, discussion of the your call numbering system ideas to continue off-list.