As far as accuracy of EMG's, I would recommend that your follow-up/future EMG's be at the same center with the same doctor/technician. EMG's/NCS vary widely between providers, so the only way to be more certain about changes is to see the same provider.

I am surprised they didn't mention BFS, also surprised they threw out "possible ALS." Sure, with unequal reflexes they may want to monitor you over time since you are young. But really, unless you start developing weakness then what's the point worrying you prematurely?

I've dealt with benign fasiculation for almost 5 years, and worried myself with the fear of ALS. I have brisk knee reflexes, but they are equal bilaterally. I have chronic denervation in my left foot, which may be related to some lumbar/sacral issues I have. My point, I guess, is I know how anxiety can get to you about this. I've struggled, and finally gotten (mostly!) to the place that I can't worry about something that hasn't shown up yet. ALS shows its face and progresses in a fairly predictable pattern, or so I'm told. Keep an eye on your symptoms, but it doesn't seem clear that it's what you have.