An article byJean Newman in the 2019 Australian Rose Annual, page 104 seems to indicate that ‘Merce’ was bred by Pedro Dot’s grandson, but it is not really clear to me. It reads (with my capitals):
....while we had been walking from one room to another in the Palace, we by chance came upon Pere Dot’s GRANDSON, Pere Dot Fabregas and his family. My hosts Pilar and Jaume introduced me to him. I mentioned to Pere that I had seen HIS FATHER’S famous rose ‘Si’ on the show bench.......On an adjoining show bench I had also admired a rose hybridised by Pere himself and he told me it was named for his wife Merce.