The readings are fairly stable, but at least they do change a bit and are thus actually measured and not just old data from memory.
I don't think that R234 is wrong - there were some separately measured voltages at R200 R201 that support that R234 is working OK. With a relacement resistor the numbers may be off a little, like maybe 100 mV, but not so much.
The numbers are more like a common offset of some 3 V for the raw ADC readings. We don't know exactly how the other test voltages are measurend, but this way it would make sense.
The question is a litlle if the offset does include a cal constant (maybe some factory cal) of some kind to effect the x1zero_2 number.
I tend to think there should be no such constant, as the other meters also show an offset of a few mV. That is more than the expected drift even over a long time for the amplifier. So if there would be a cal constant involved the zeros should be much better. For diagnostics it also makes sense to give raw reading with as little cal constants included as possible.
It is still a quite good values for the nominal values of the resistors - so the resistors seem to be rather high accuracy (e.g. better than 0.1%), but still not impossible.
So the offset is likely the reading of the ADC without any individually measured offset constant, just a common constant somewhere in the firmware.
The fast channel offset may be actually the difference to the precision channel. It would be really odd to have an offset at the amplifiers ouput only for the precision channel and not for the fast channel. A more ouput side offset would be more an ADC problem than an amplifier problem.
The R200/R201 measurements also supported that the amplifier was near zero with a shorted input.
It would than still be odd to give the other voltage readings also as raw values without offset correction, but who knows.
So the 10 V instead of 7 V would be because of the 3 V offset added and not a factor 1.4 in the scale factor.
A large offset at the ADC may also effect the linearity (also visible as DNL) of the ADC. For a quite check of the linearity ( more local, DNL like) one could use a slowly drifting votlage (like a large capacitor slowly discharged through a large resistor) and see if the measurend voltage gives a really smooth curve. The 1PLC data would be the more sensitive to the rundown part than higher PLC.
A 3 V offest at the ADC would also reduce the measurement range somewhat. So does the meter read OK to some +12 V or where even the upper limit is ?