The seedling number (84J3T403) of this variety shows that the cross was made in 1984 when Lynn Collicutt was the breeder at Morden Experimental Station.
In my yard in Ontario (zone 5b) Morden Snowbeauty repeats as well as most other shrub roses. That is to say, the first flush in spring and the last flush in fall are always the best and there is sporatic flowering in between.
Snow Beauty is hardy in the Canadian sub-arctic, north of 60ยบ ! It survived a bitter winter, planted on the shore of the Great Slave Lake, without any protection or help. And it's blooming beautifully again this summer.