I'd agree with you on every point, but for a few things, I originally thought there were Sika here, and was told otherwise. Here's a distribution map for Sika. I'm smack bang in the centre of the area where they don't occur.
I'm no deer expert, far from it, but these are right slap bang in the middle of my survey area, which here is quite a small area. As a zoologist specialising in sole species study, I have to liaise with the local experts. The foresters and mammal experts that work that area only report two deer species, fallow and roe. I will pass your post onto them all, and the pictures and see what they say. All I can say, is that I have never seen a buck with Sika-like antlers. They have all had very characteristic fallow antlers.
I've seen Sika many a time further south in the UK and they all fan the hairs out on their butts when alarmed. These by me, don't. And most lack the dark stripe that Sika seem to have.
There aren't any deer farms near here that would suggest an escapee or release, but it will be interesting to see what the locals say about it. That last thing this area needs is another introduced deer species. Fallow are over populating the area as it is.
Is there any evidence of cross species breeding?