Hi Porter - Were you tested for T1 in 2003? Didi you carry any extra weight at that time?
Misdiagnosis (in both directions, although more commonly as T2, when in fact late onset, slow developing T1), is disappointingly common these days. We see a steady flow of folks diagnosed T2 (in particular), who struggle on, doing their best to contain their condition, whilst ending up on an escalating package on medications, before the relevant tests are conducted.
Sometimes those folks are atypical for T2 - younger, slighter, and some are abetter fit to the percived typical T2 - a bit older, carrying some excess weight. Those being misdiagnosed T1, when in fact they transpire more likely to be T2 are very usually younger on outset, although I know of at least one, who transpired to be T2 in her 60s.
The most common cause of hyperthyroidism is an autoimmune (AI) reaction. Once an individual has one AI, they are statistically more likely to develop more, such as T1.
Now you have re-diagnosed, have you started on insulin therapy? Many forld who end up reclassified find they feel so much better once they start on the proper treatment for their condition.
Really good luck with it all. It sounds like you've had a rough ride.