Although most 'missing' numbers and letters are due to 'filled dies', your photo, (a bit blurry) shows damage on the '1' in the date.
image is a tad bit out of focus, but I believe yours is just damaged. Coins get banged around all the time (in purses, cup holders, cash registers, sidewalks, parking lots, etc.) and things can get banged up. If there was a hit directly on the middle of the 1 then it could have just been banged off.
thanks for the better image Looking closer at it, you can see a strike mark stretching from the lower part of the 9 through the 1. Of course, this could have happened from multiple strikes too. We don't know as we didn't cause the damage. Looks like damage. if you look at the entire coin, you can see damage, wear, etc all over it. Even the lower part of the first 9 was damaged/cut off.
Try to find a 70 year old anything that has been utilized and passed trough many people that doesn't have some scars or damage from wear and tear. the wear pattern shows it has in circulation quite often maybe in parking meters, gumball machines, pockets, collection plates, purchases, etc. If only we could look as well after 70 . ( well besides me of course Jim