[Significant recombination never happens in an open cell.] This is the truism that the CF community holds onto for dear life.
No, it is a fact that is easy observed using techniques that every electrochemist has know since Faraday's time. 19th century techniques are sufficient to measure recombination. (Obviously this must be true, because Faraday measured faradaic efficiency, which is to say the lack of recombination.) You measure the make-up water, and the gas using a bubbler and an inverted test tube. All electrochemists check for recombination. Fleischmann, Miles and others reported the exact amounts in their papers. The amounts are far too small to affect the conclusions.
Furthermore, even if there were 100% recombination, the anomalous excess heat often far exceeds the heat that would be produced by this recombination.