It would be nice to have a picture of the actual medal on both sides. As it has been said before, there are thousands of copies out there. Some are bad copies, but some are very good, like the so called "Spanish" copies floating nowadays on Ebay.
A WWI official award would have been manufactured by Godet, Wagner or Friedlander. You can distinguish them by the workmanship and certain details on the eagles, etc.
These links will show you authentic Wagner, Friedlander and Godet PLMs
The Typology of the Pour le Mérite
The Godet made Pour le Mérite
An official award, pre 1918, is very difficult to find. They are selling over 25k nowadays, when you find one.
I hope you have a real one! Would love to see a photo.