Well, your effect might be bounded:
(1) in an open cell, if H2 + O2 is out of cell is measured accurately and compared with ttal electrolytic current that can limit available recombination (though not other possible cal shift causes)
(2) in a very low loss mass flow cell calibration is relatively insignificant, and your mechanism is bounded by the cell losses, and practically significantly smaller than them. (I know this is cell losses on total power in, which may be lagre compared with claimed excess).
(3) in a cell with good enough isothermal barrier your effect is bounded
i agree, they have not looked in detail at which results are so bounded.