Thanks very much for looking at my query.
I think it may be something else.
At one time I had a default value of 12.5 in the DecimalField of the model. So the the initial value of of the form field was always 12.5, no problem there.
My issue is that for existing products I expected to see what is the present value , instead in the stock and pricing form I always saw 12.5.
Hence the reason why I removed the default, hoping that when I looked at an existing product I would see the existing value of vat.
Instead I just see "----'.
The dropdrown works as it should. See pic below.
However I don't see present values.
I have also changed my model as per the link you suggested but no change.