Genghis,
CS-23 and CS-VLA make interesting reading regarding seat weights.
CS-23 goes into great detail about loadings in various directions for seats and seat belts.
However, the general weight on the seat used "to show compliance with requirements" seems to be just that - a notional weight that is used to show compliance - not a limitation. If it was a limitation then loking at the part where minimum weight is specified, if taking that to be a restriction one could never fly the aircraft with that seat empty!
Since minimum weights per seat may be specified to show compliance with the requirements, are they saying that seats can not be empty even if the C of G is within limits?
My reading of the specified weights (which are only options under CS-23) are that they are used to prevent designers using overly light individuals to acheive unrealistic figures.
However, that aside, if the CAA say that it is a restriction then it is a restriction and organisations interested in flight safety need to consistently and constantly send out a clear message that the rules are to be complied with..........until they can get the rules changed.
Regards,
DFC