Oooops - thanks for pointing out my AOT logic there. Note to self: don't post after returning from a night flight!
The other reason for the disparity of bugs on the Machmeter vs the flt envelope is whether they relate to the first or second M/CG warning. I can't remember and don't have the manuals to hand. I do recall that it was more accurate/practical to monitor the speed-driven limits on the CG indicator rather than the CG-driven limits on the machmeter.