Ok, to round this off:
1) always test your keyword matching etc on Overture.com first, not Yahoo!
2) to see which partners use broad match, have Overture and the partner (e.g. Yahoo) side by side in two browsers and compare the PPC results.
I've never seen a list of who uses which keyword options from Overture.
3) I've noticed sometimes keywords still don't appear when you'd expect on broadmatch.
I think - never had this confirmed - that Overture use a system that "scores" the match. So if you are bidding on 2 keywords out of the 3 searched for, your ad is shown - but if you are bidding on 1 out of 3, it isn't. Anybody confirm?
4) Google doesn't provide a list of which partners use which options either, but I beleive they all use all three types of keyword match.
So - bid on all the variations is my advice...