I may be wrong, but I believe that that culture came from a mixed culture. Up until Emil Hansen isolated Carlsberg Unterhere No. 1, lager, like ale, was fermented with mixed cultures that were bottom cropped. I believe that up until the Berlin Wall fell, Pilsner Urquell fermented with a multi-strain culture that may have contained one or more cold-tolerant Saccharomyces cerevisiae strains in addition to several Saccharomyces pastorianus strains. That is why there are so many cultures that claim to be Pilsner Urquell’s strain. They exist because people performed single-cell isolation on a mixed culture.