BOAC,
Bobcat - I cannot see such a trim restriction limiting the cg envelope - I reckon we should be nowhere that trim in normal flight, not even on an autoland flare?.
One can always argue that a CoG set way outside (forward) the envelope will not be dangerous because it's possible to back-trim the way it is on this aircraft. When just considering trim (CoG outside the envelope is always dangerous).
As always, we need to ask: "When do we need full back-trim?" If the answer is "NEVER", then restrict it. Just like "When do you need auto-retrard on a single channel approach?".
-Bob-