Oh, by the way, many aircraft do not have any trim tabs at all - most
gliders use springs in the control circuit, J-3 Cubs move the
horizontal stabilizer, the F-4 I used to fly changed the neutral
position of the whole flying tail, etc...

Thanks, presumably on behalf of many, for an excellent overview.

BTW, in the case of the fully trimming stab on the J-3 Cub, DC-9, and some
others; as well as the fully trimming tail of the F-4, Mooney M20, and
others; it does seem hypothetically possible that the control authority
could be influenced--but that would be a side effect of obtaining a design
goal, rather than a feature in itself, and certainly outside of any area of
expertise which I might have.

Peter