A and C
The majority of Seneca owner go 1999KG to save on airways charges etc! To go any distance with half reasonable amount of PAX which would require using airways would mean exceeding the 1999 KG but NOT the design limits.
As such a lot fly over the 1999KG illegally.
The manuals are written up to the lower weight but the original manual if it was registered at the lower weight would give the data.
Just struck me that it would make an interesting court case if there was an accident other than the obvious technical paper infringement
Pace