I don't believe you suddenly had chronic denervation show up in the last month. The greater precision, at the expense of more abnormalities, is part of going to somewhere like Mayo. Equipment, operators and protocols for EMGs differ.
However, of note, the abnormalities are localized, not widespread. This, coupled with your symptoms, is, as the report says, not worrisome for MND. So what I'm hearing is that you have subclinical weakness/mild nerve damage in your L foot and nothing else really forming a systemic picture. Injuries, compression and other causes of nerve damage can go back to birth, so just because you don't remember anything doesn't mean it didn't happen. They can also occur in sports, sleep and on a couch.
Remember also, that diagnoses are not made from EMGs. They start from the clinical picture.
It's good to know the genetic picture, and to follow up if your issues progress, but the odds are still very much in your favor.
Best,
Laurie