There is likely a MI law that has an Oct 15 deadline”
It’d be great if a freeper who is a research whiz could nail that down....
I speculated that just to be charitable to the author, as in Oct 15 not being a date just picked from air. The author of the article is in the best position to divulge the authority used, for MI having an Oct 15 presidential primary filing deadline.
Once I find a source that I think is credible (in this case, a website maintained by the state of MI, recording its legislative activities), I figure I'm accurately informed, and that's the end of my chore. Sometimes, like this time, I do more by posting my finding and source for others.