Didi
Problem if your BG is raised to 'pre-diabetic' stage at a pre-op check this could be caused just by the stress of facing a pending operation, or the effects of the condition leading to said operation and/or any medication you might be taking to treat the condition leading to said operation... So after the op and recovery period you could have returned to normal blood glucose levels never to have a problem..
Problem with how long an individual had T2 before being diagnosed is a 'could have been' between 5-10 years... Before symptoms appear.. But it's only a could though..
If you look at T1's it's assumed that it happens pretty swiftly, but does it they really don't know at what point the cells starts being destroyed.. My husband said with hindsight his first subtle symptoms started around 8 months before he was diagnosed...
In my case my T1 was picked up so early, that it was thought I was T2!