You know, your discovery (or whosever's) of the blue stain in Majdanek cell 14 is probably more consequential than anyone has given it credit for.
Most important is that it tells us one accidental exposure was enough to cause blue staining. This puts it in the same category as the two churches that developed blue stains after replastering and disinfestation, which Rudolf has built chemical arguments around. Strong supporting evidence for him.
It also may have some bearing on matters like exposure time, concentration, proximity, and diffusion. Imagine that the room had a door which was left closed for hours or even days before the Zyklon leak was discovered. It would then be somewhat surprising that the Iron Blue formed only in the corner. On the other hand, if the doorway was open to fresh air, it would tell us that Iron Blue can form even when it is being drawn away by diffusion. I'm speculating, but there could be something useful here.
One other thing. We know that fresh plaster is one of the important factors in Iron Blue formation, so it's possible that this leak is more likely to have occurred under German control rather than under the Soviets.