Carl,
Yes, I've seen this type of progression before. We had one guy at our support meeting that started in his right arm, then went into his right leg. His truck got weak next. He could still walk but one side seemed like it was dragging and he needed a walker. I only went to support meetings in person for a couple of years but he kept progressing on his right side. His left arm was very strong.
The only thing for sure with this disease is that it's so different in each person. Mine started in my left foot but progressed very slowly. After two years it seemed to hit everything at once but very slowly. I stopped progressing for nearly two years, then it started speeding up on my right leg and left arm. Both lower legs are atrophied now.