Leslie, to answer your first question the only study I can think of that might address your question is Dr. Buck's on the responses of specific cultivars to different races of daylily rust. There was also another publication that rated cultivars at two different times of year, and I think in two different years - I'd have to check it again for the details if that's what you're asking. I believe that one was incorporated into the ATP ratings.
Rust will also vary depending on other factors like environment.
