It does not sound like any system I have ever come across, to somehow have the accumulator valve electrically activated.
It might make a bit more sense if there were holes present in the structure to the rear of the engine where the 'optional' unfeathering accumulator would be mounted.
As to how evidence of the previous fitment of unfeathering accumulators tells us that the aircraft were looped and rolled on their test flight following construction, I must admit I am lost.