That is going to be a rather difficult thing to determine. There are numerous strains of black spot in the US. Not all affect every rose, nor are all of them in the same location. What affects a particular rose in one location may not exist across the country, so the rose may be highly resistant to the strain or strains of black spot occurring where I live, while the same rose may be highly susceptible to the strain or strains of it where you live. Or, vice versa. If you notice, you will often find the comment "highly disease resistant" on a rose's page, yet in the comments you often find that it is highly susceptible to one or more diseases in the commentators' gardens. William Radler, the creator of Knock Out, literally collected black spot from around the country in hopes of gathering all the various strains possible so he could expose his seedlings to as many of them as possible. This permitted him to select the healthiest ones to the most strains. Even then, Knock Out has been found to be cleaner in some areas than others. The best information should come from those growing the particular rose where you live. At least then, you could make a guess whether it is resistant to the strains prevalent where you are. Good luck!