It’s often been said there are two types of astronomy, the study of the Crab Nebula and the study of everything else.
Interesting paper, the link below explores the precursor mass, I did wonder if it would have been mentioned in the paper above, but then again there has been so many papers concerning M1 it’s not surprising not to have seen it mentioned.
https://iopscience.iop.org/article/10.1088/0004-6256/136/5/2152