Hello Bebo, I hope that soon others will reply to you with more information. I am new to MG so I do not have much to offer you.
What I did learn is that all the testing that was done for me was normal or negative until we got to the final test -- a Single Fiber EMG or SFEMG. For me this was positive and I was classified as "seronegative MG". It doesn't necessarily mean you are any better off health wise, there can be just as many problems if the blood tests are positive or negative. My neurologist says there are things going on in MG that just can't be tested but they are there.
I don't know where you are in the world but there are not too many places that have doctors trained in SFEMG. And as with any test you will want it done by a doctor who is very skilled and experienced so there is no chance for false results.
I hope that this information is helpful.