DCI Jones recorded in his pocketbook that he observed spots of blood on the stairs, but this blood was never tested to establish that it was indeed blood or of what group/type.
I agree most likely Nevill's, but we don't exactly know where on the stairs the blood was observed. I appreciate DCI Jones will have been experienced in observing blood stains, but unless it was tested, we can't be sure it was blood or whose it was.
I don't accept it is conclusive that June was actually shot in bed. I understand completely why most have come to that conclusion, but I think it is possible she wasn't and the blood on the bedclothes and the bullet hole can be explained differently.
The reality is:
We don't know where on the stairs the blood was found.
We can't be certain it was blood.
If we assume it was blood, we don't know what blood type.
June need not have just been in the bedroom, though I accept she was found there and she must have been shot while in the bedroom.
I am just mooting the possibility that the blood on the stairs could be someone else's.