Sure, I could separate with multiple libraries. Buuuuuuuut...
On one hand, I have about a dozen book sources which I want to keep separated, so a-library-for-each gets unwieldy pretty quick.
On the other hand, calibre2opds can't merge multiple libraries into one opds directory so configuration on my reader devices gets complicated.
And, on the gripping hand, the OCD afflicted software engineer in me wanted a configurable solution which would also consider Series information and whatever the user might consider necessary
. So, main reason is my OCD