The real reason? The die that struck your coin was over polished. When a die is polished, what is affected? The fields are reduced. With the devices tapered, the widest area is the base of the devices. When a die is polished, the fields are reduced on the die. With the reduction of the fields, the devices get smaller in size:
The devices loose details.
Isolated polishing to remove die events, thin the devices size:








What was my
first clue that this is an issue with the die polishing? Note the first image? Where is the Master Hub Doubling on the '2'? It is gone:

Note the inside area of the '2'. The die polishing removed that mark. The
second clue is how small the '2' is compared with a normal coin. Extreme die polishing can alter the dies so much that a lot of the devices tend to go away:

That is the cause and why the devices look different to your eyes. It is not a doubled die, not a small date (which there are none that year). It is a die event from over polishing. When they are reduced, it should also be the first thought of the cause? Reduction of the fields on the dies.
CoopHome:
What causes the devices to be smaller or weakened on the designs on coins? field reduction to remove/rescue die events. Die dents,
Feeder Finger Damage to keep using the dies. thus the missing devices on coins. they are all the rescue efforts to extend the dies. (the mint doesn't realize that we figure this stuff out)