But you are quite right. Whilst Iron was the biggest, there were others. Apart from Iron there were at least another dozen or so. There are fragmentary accounts of the trials of eight of them - and spying doesn't seem to have entered into it. They would have made very poor spies: most of them could't speak French or German, they could only move about with difficulty, and had no means of communicating with the Allies.
As I pointed out earlier, spying as a justification or pretence was not needed by the Germans. They had been caught behind the lines outside one of the many windows of opportunity they were given to surrender. That was sufficient. Why charge them with something - spying - against which they could mount a plausible defence, when they were clearly guilty of another capital offence?
Yes, I realise that spying was a risible justification and did not mean in any sense to suggest that such a charge was plausible (indeed I don't think that I did). My point was solely that arresting a soldier in 'civilian clothes', as opposed to uniform (as queried by Grumpy in his original post), was sufficient justification under the Hague Convention to have a man shot, over and above the failure to observe the German authority's conditions of surrender. In short, it was a trumped up charge that was apparently used on some occasions, although I do not know how many, or how true, such reported incidents were. I only know that I have read of them in several contemporary accounts. I have no knowledge of the case of the 'Iron 12' and therefore make no comment in relation to it.