I have a bunch of comfrey that I've been propagating on my property. It's is some sort of infertile Bocking variety, but I don't know if it's Bocking 4 or Bocking 14. Among many differences, Bocking 4 is commonly used for fodder and has a higher protein content and Bocking 14 is better for biomass but contains more compounds that make animals sick if eaten in large quantities.
My neighbor has horses and the fence between us is often plagued by blackeberries (yes, a plague here in Oregon) and other weeds and I've been thinking of planting the Bocking 4 variety of comfrey on my side of the fence. I'd like to have the Bocking 4 so the horses won't be tempted to eat the more poisonous variety. If I knew I had the correct type, then I would simply propagate it, otherwise, I might opt to order some Bocking 4 cuttings.
I honestly don't know, but hopefully my reply bumps your post back up & someone well-versed in comfrey will see it & educate us.
From my understanding, I he flower color is indicative of the variety, but can't remember where I read that.
Your's appears to be more upright and uniform compared to my plants. Mine tends to get more sprawled out over the ground, and only grows taller when it sends up a stalk to bloom. It also tends to keep fewer leaves, that are much longer/wider than the one in your pictures, with only the leaves on the flowering stalks being narrow. Not sure if that's because they're different varieties, or just growing in different environments... I have no idea what kind I have, it was just labeled "comfrey" at the nursery I got the original plant from.