Becky, the cut leaves are not a point of entry for rust, rust gets into the leaves through the stomata. What can happen is that when a plant is cut back any loose spores can fall down between the leaves and cause an infection later. Also a plant that was infected before arrival may not show any pustules for a significant amount of time after receipt, whether it was treated with fungicides or not (and fungicides don't eradicate rust which is why we still have it).
It'll be difficult to separate the apparent variations from effects of environment on rust because the favourability of the environment for the fungus will vary during a year and from year to year, and even among plants in an individual garden in the same year. The balance of fertilizer or nutrients already naturally occurring can also make a difference and that's another variable. The same cultivar in one part of the garden may get rust while in another part it gets it less or more, simply because the environment differs enough to affect the ability of the fungus to infect. With plant fungal diseases it is all about the environment, e.g. how long the leaves stay wet at any one time, what is the temperature, what is the light intensity and so on. When the leaves don't stay wet for long enough there will not be any new spore germination, for example, just like a plant seed doesn't germinate until planted in moist medium at the right temperature.
There's also the effect of environment on resistance genes, I'd have to look up the exact details again but where it's been investigated in some other rusts it was found that there was a temperature "switch" that turned on or turned off the genetic resistance capability depending if the air temperature was above or below that temperature point.
One thing someone mentioned in this thread or another is fall clean-up. Sorry I forget who and if I try and go back to find the post I'll lose what I just wrote. In areas where rust is borderline for survival, like USDA Zone 7, removing all the foliage in fall and not using a protective winter mulch should give the garden a better chance of being rust free the next year (unless new plants are brought in). The less foliage remaining green through the winter the better, but of course it still only takes one plant staying green to potentially carry rust through until the next year. That won't help you, though, Becky.
