Hello, Lyn! Unfortunately I haven't any official information. All the informations I have come from nurseries that sell this rose. As far as I realized this rose was found in Germany near the city of Kassel. Most sources agree this rose is a centifolia and refer to it as to a unique remontant centifolia. But the Belgian Daniel Schmitz mentions this rose as non remontant. http://www.danielschmitz-roses.com/rosiers-du-temps-passe/centifolia-typ-kassel Perhaps he has not the real Typ Kassel, but another centifolia. Our member Pascale Hiemann wrote above that his Typ Kassel don't rebloom. But maybe he has not the real one too.
My one more version is that Typ Kassel itself could have some varieties, sports or mutations during further reproduction that are more, less or non remontant. Or maybe they could reverse to the true non remontant centifolia. I would try to find it out and any official sources too.
I was interesting to try this variety in Russia it's because I got one plant from Rosen Schultheis to test it.