Per my post 35 above, a German historian and guide at Dachau explained to me how the SS used Dachau to test out prototype gas chamber systems and processes. It was there that they determined that camouflaging the gas chambers as showers was the most effective way to get the prisoners into the chamber without a fight. To be clear, thousands of prisoners died as part of these tests.
Perfecting the execution mechanisms and processes for the actual death camps was part and parcel of the Dachau camp’s “business as usual.”
It sounds like the prisoners executed prior to the liberation were residents of the camp. They would have been under no illusions as to the purpose of the “showers.” They may have been the labor used to empty the showers and feed the crematorium.