Okay well I'm not going to worry too much about it. I see the fact that it reads the same as an external 50uV signal for both 100KHz and 25KHz as a bit of a bonus if anything. The board is a 'B' variant, not sure if they made other changes I haven't found a schematic for the 'B' version just the plain PB-1547 but it does seem to mostly agree with that schematic I think. And apart from some slight reduction in the calibrator signal on 160m, which I think might be something else, on all other bands it is a similar level. Quite remarkable that it could be faulty and that good!