Thank you all, for your responses.
kovidgoyal seems to be entirely correct (not surprising), and so I am boggled at how I came to this pass, as I know for sure I checked all the ADD options on many occasions, before developing my script some months ago.
My old laptop is running the exact same version of calibre, as my Netbook, and adding using the single folder method, worked flawless yet again. Something is missing or I had a hugely dumb moment (can't rule that out at my age).
So I have adjusted my script (but not had time to fully test yet), to still work using the OPF file, but then grab the parent folder to add the ebook title and all formats. It uses the OPF metadata content to check for an existing entry, and fails to add if one found.
My apologies Kovid Goyal for interrupting your good work ... or whatever it is you do in your downtime. Much appreciated.
P.S. Waiting for darkness to fall so I can sneak back unnoticed to my hermit cave.
