Great idea on the acetone.
I would have to say I agree that the mint absolutely wouldn't have working hub dies from two separate years (1956 & 1958) in the hubbing machinery at the same time.
MD can definitely give you an "Echo" effect that might be mistaken for a second number, especially with gunk interfering with a clear view. That MD "Echo" shows up well on the 195. The acetone bath should remove the gunk around the date.
Words of encouragement are one of the major food groups.
We need to consume them regularly to thrive and grow.