In the SEX amp with the C4S load, the plate current and cathode bias voltage are fixed and the plate voltage wanders. Lower plate voltage in that situation means more emission, so the drop from 70V to 66v indicates that the tubes are breaking in and working better than when you first tried them.
In the Crack, the 6080 grid voltage depends on what the 12AU7 is up to, so the voltages you have don't really mean much without knowing the voltages on terminals 1 and 5. If the voltages on the plates of the 12AU7 do not move but the cathode voltages on the 6080 increase dramatically, that is also a sign that the 6080 emission is going up a bit. If you find that OA and OB on the large board go down and get really close to OA and OB on the small board, that's a dying 6080. If you find that the OA and OB voltages go up on the big board and also that the OA and OB voltages on the small board go up, that has more to do with the 12AU7 wearing a bit.