Answering not as a qualified Forensic Pathologist but as a Technician assisting many years at autopsy I would answer the question if a subdural haemorrhage can be missed at autopsy as being unlikely.
In fact the autopsy would be the gold standard for determining if a subdural haemorrhage existed. I think the more apropriate question would be can a subdural haemaorrhage be mistaken for something else such as lividity, or related to post incinerations.
Subdural are acute or chronic. With chronic they usually found in elderly and instead of fresh and appear like blackcurrant jam the chronic subdural is tany brown due to the age. Under the area the brain will be depressed. Some 'lesions' are small in volume. The heat haematomas I mentioned associated with incinerations are usually extradural.
textbooks discuss the volume needed to create a space occupying lesion consisting of around 30mls + which leads to irritation and neurological signs and symptoms.
I am not a qualified Forensic Pathologist and the answer is based on observations at autopsy.
