i do wonder if deuterium is involved in these experiments and not protium if we can get a similar Z evolution if some kind of induced beta decay is responsible or normal beta decay if heavy isotopes of the nucleus are generated. But I suppose it's a bit of a stretch to speculate that. Even deuterium would struggle to get over the coulomb barrier of these heavy nuclei.
Yes, light hydrogen controls would be relevant here. The paper I linked to does not mention any such controls. I vaguely recall them being used in one or more studies elsewhere.
Deuterium would indeed struggle to get over the Coulomb barrier. Where's the energy release needed to make that happen? That does not prevent people from speculating that there's some kind of multiple deuteron capture going on. There are several difficulties with this suggestion beyond the question of the Coulomb barrier, including the question of why there are not Z+1,3,5 transmutations as well.
Do we know if free neutrons were also observed?
It's an interesting question. I suggest digging into Iwamura's papers and reading for that detail. If there's been any attempt to measure neutrons, I don't suppose the number were very high.