An important detail which may already be known to Mizuno, in the context of the recent breakthrough is the possibility of spectral line emissions in the Balmer series particularly the Balmer alpha line at 656 nm or of course any of the most energetic lines.
At least one of the reactors has a window so it is possible that spectroscopy has been done already. The IR lines -Paschen/Brackett – would be expected and could be informative when analyzed but the alpha or higher Balmer series lines would be unexpected at the low temperature of this reactor since the mass energy needed for the lowest transition, the Balmer alpha line is ~1.9 eV. If there was any kind of nuclear fusion reaction going on – there would be broad Balmer lines. and If there are few, then nuclear reactions are unlikely. AFAIK - Balmer line broadening has always been seen in cold fusion when it was looked for. If gain derives from Coulomb explosions with a signature of 630 eV or from Mills type reactions, then there should be significant Balmer broadening - so the presence of strong emission lines, in itself, does not pinpoint the exact source of gain.
