I believe the experts are not too clear about it, either.
Elsewhere on this forum I have read of one seemingly clear-sighted expert who prefers to talk in terms of auto-immune diabetes and non- auto-immune diabetes.
But auto-immune diabetes - or type 1, if you prefer - sometimes takes a while to fully develop. (The insulin producing cells in the pancreas aren't always killed off in one go.) This may be the reason why some experts are inclined to speak of 'type 1.5': it is perhaps just a stage on the path to the full development of the auto-immune form of diabetes.
