There are different strains, but it is debatable how different they actually are. What has happened is that different nurseries, such as Van Well or C & O, have their own scion wood blocks and they will tell you they have selected the best scion wood contributing trees over the years, actually over the decades. Both of these nurseries take their job very seriously and you would get good Bosc wood from either, as well as Columbia Basin or Willow Drive or other nurseries which cater to the commercial grower. There is no difference between Burre Bosc and Bosc. Some just drop off the "burre" part. Indeed "burre" might mean "pear" in French or something, I don't know. There is a russetted strain of Bosc and it is what commercial growers prefer, because they want to sell Bosc as a russetted variety. The reason they want to do that is because Bosc russets anyway so why not have it uniform appearing. Again, cosmetics in commercial orcharding. If the ones you bought taste different there could be many reasons for that. I think Bosc is a tremendous pear to grow for yourself, but it will FB.