MG is not one disease.
There is autoimmune MG and Congenital/genetic MG.
Each of those can be further subdivided. Autoimmune to AchR+, MuSK+ and yet unknown antibodies. (some also would add Rapsyn, and other antibodies that have been found in occasional patients).
Congenital to: AchR-fast and slow channel, DOK-7, Rapsyn, MuSK, CHAT and many more. Some of which have not yet been discovered.

The course, response to treatment, and prognosis of each of those is very different. Some have a very slow/intermittent course, others have a more hectic course, and yet others have a gradually progressive course. Response to immune modulating treatment is also variable, as is response to AchE inhibitors (such as mestinon) and other symptomatic treatments (such as albuterol, ephedrine, 34DAP and others).

Further more, the same disease affects different people in different ways. The threshold to seek medical advice is also different. Some people would come to their physician with every minor ailment and others will seek medical advice only when their life is in imminent danger, and there is a large spectrum in-between those two extremes.

I am not sure that non-specific symptoms of fatigue are MG-related. It is very likely that there is some element of what is called "recollection bias". this means that you interpret the past in view of the present.

What I mean by that is that if someone for instance has a heart attack, he is more likely to think that chest pains he has experienced prior to that, after exercising in the gym, were in retrospect ischemic heart disease.

On the other hand, a young and healthy person, asked the same question would more likely think that those are due to straining his chest muscles in the gym.

That is why I believe it will be very hard to know the answer to your question.

Also, take into account that patients who are rapidly diagnosed, have an excellent response to treatment and lead a nearly normal life, are less likely to participate in a patient support group like this one. So, they will be significantly under-represented in your poll.

I can tell you my own experience (even though it is probably on the extreme of unusual). I had the shortest diagnosis of MG (before I myself realized some thing was wrong) and the longest (20 years later). I had a spontaneous remission (that lasted for 15 years) and a refractory disease that doesn't seem to respond to any commonly used treatment. 20 years ago my illness didn't exist (because MuSK was discovered 10 years later).
This also explains to you why I chose the pseudonym Alice.