Thanks very much Patricia - that is much closer. Duehrsen didn't say the pollen parent was a simple cross of the two roses but rather, a hybrid seedling with both R. gigantea and Cecile Brunner included in the gene pool. He said Cecile Brunner was 'one of its earlier progenitors' so we know there were additional un-named roses in its lineage.
The notes you have added make this clear.
I am unsure of what the system allows you to put in the parentage field, and how you get around these instances when you know some, but not all, of the roses that have gone into making a new variety.
I'm so glad the rose is doing well for you. The ones here are too. I've found it a quietly determined rose for its first years - more and more exuberant as it becomes established.
I noticed that the date of introduction in the earliest references is given as 1947 and in later ones as 1948.