C peptide will show how much insulin you are producing,
There is also a fasting insulin test, this also shows how much is being produced. Too much would definitely show type 2, too little could be either type 1 or 2.
High counts of anti GAD are often present in large amounts in type 1 at diagnosis.... but so are other anti-bodies, they are very often present in LADA .They're also present in lower amounts, in some 'type 2s' (by what definition?)and in some non diabetic relatives of people with type 1 and several other diseases. However, its not definitive either way as they are not always present .
Twelve years does seem quite a long time to remain insulin free,(for LADA) however only a few years ago people didn't distinguish between type 2 and older people who needed insulin within a few years of diagnosis. I'm sure that more and more sub types will be distinguished.
There are other types of diabetes, in particular MODY.which often develops before the age of 25
is
strongly inherited . Jenny Ruhl is a MODY and there is a good account on her website .
Genetic tests for MODY are available in the UK from Exeter university but are expensive.
As to the overnight production of glucose, you're both right. In the normal body during fasting the liver releases glucose to stop a drop in blood glucose levels, as the levels rise its action is stopped by insulin.(good diagram in
http://health.howstuffworks.com/diabetes1.htm
If there isn't sufficient insulin (as in type 1 or in type 2 with exhausted beta cells) then blood glucose levels may keep on rising.
In people with type 2 diabetes, who suffer from insulin resistance (and therefore dysfunctional regulation of blood glucose with insulin), the liver often has a tendency to produce sugar when not really needed.
http://www.defeatdiabetes.org/news/view.asp?id=54652
Unfortunately there are no simple answers
