I wonder if the "X times refined" business is just more advertising gimmickry? Years ago I worked in a natural gas processing plant where we "refined" butane. Actually what happens is there is a series of fractionator towers or distillation columns, if you will. The LPG flows from one to the next with the high ends going out the top and the heavies flowing from the bottom to the next tower.
Ours were: Deethanizer, Depropanizer, Debutanizer, and Iso-Debutanizer, in that order. I guess you could say our butane was triple refined. If you counted the pre-distiallation process, you could say 4X refined. None of it was actually filtered, which is not to say it couldn't be. I agree with the opinion above that the important information is impurity in ppm. I've found with butane it is not best to go cheap.
As far as I've been able to tell, the standard stem with no adapter never touches any seals - at least on my Petersons, my Imco, and my Radio Shack butane soldering iron. Vector cans have come with metal stems and with plastic stems.