I can tell because normally as you level up "Bind Demon", the attachment slots just appear in your inventory, wether you have a fitting seed or not. That's not what happened for me several times by now.
Most of the time, the offhand slot just doesn't appear and I don't find any demons for it either.
If I'd have to tell about any weird stuff I did with those characters then it would be that I de-leveled the "Demon Seed" skill before spending a point on "Bind Demon", because I feared the game wouldn't realize that it is a world-changing skill itself.
Also I'm playing as a ghoul.
Apart from that I saw that I got my second ring slot 1 level too early.
Good luck with that!
