I'm glad they think they got it all with good margins. Unlike CeeeeCeee my thyroid has been bonkers since my surgeries 4.5 years ago. Some of it was due to the rapid weight loss I experienced. I printed off a graph of my weight for the last 9 years of office visits and took it to the endocrinologist. I marked important events, like the surgeries. She was glad I did so. In other words your right, weight is a big part of it. (The doctors didn't know graphs could be produced from their on-line patent records program. The accountant never wastes an opportunity to create a graph.) So there is a reason they weigh us at every appointment. It sounds like your weight has been steady so hopefully the dose is correct. You will know it when your metabolism declines, unless you have other health problems that include chronic fatigue.
If your insurance company forces generic synthroid on you please have your doctor specify that you need the name brand. I found out the efficacy can vary 5% either way and was 10% until recently. If generic is ok please watch out for changing of producers as well.
Great catch by your GP!