Howdy folks, and thanks, Mark - I'm glad you like the dagger even though it's giving you headaches!
Here's a picture of the dagger in question:
My original (and current) estimation is northern African somewhere ... the Berber guesstimate was Tom Hyle's thoughts on the origin.
I don't think it's a shabriya variation, the blade shape is really quite jambaic, and even the most extremely curved of the sabriya (nice collection!) doesn't really come close to being the same.
As to Iraq and Marsh Arab - also, I think not. Their hilts are sort of triangularish as shown in Mark's new whatsit, but the Marsh daggers really have a more dart/arrowhead shape to them rather than the clearly defined triangle.
Here's a Marsh dagger shown along with a modern stainless-steel bladed repro:
The blade curve/shape of the Marsh jambiya is quite similar to the blade on Mark's Mystery, but I think the pommel shape rules out Iraq in specific - although now that I look at all of these pictures together I'm certainly willing to narrow down my estimation of "nothern Africa" to eastern northern Africa (ish!)