I didn't see Mountaineer Pride listed as a hybrid in the source where I got it (Southern Exposure Seed Exchange), but it says that WV 63 was used "to breed two new, larger tomatoes, with disease resistance now including septoria leaf spot." Since it didn't say that it was an F1, I assumed that Mountaineer Pride was a stabilized cross, of WV 63 with some unnamed variety.

I also think they are OP varieties. Otherwise, I wouldn't try to grow them. Today, it is already full of other hybrid varieties that are resistant to potato blight and their seeds are also available in the Czech Republic.
Vladimír

I've tried every "Septoria Resistant" variety that has been released in the past 10 years or so, and Mountaineer Pride (and I presume it's sister, Mountaineer Delight) are the most resistant I've found. I follow the suggestion to grow it away from other susceptible varieties. I grow it in a 10 or 15 gallon container, and it produces very nice, flavorful tomatoes. Medium sized, I would say a "pinky red," and not too tart. This one is a keeper.
Available from Southern Exposure Seed Exchange.