Looking at the photo's of the checkering, it is very evident that it is a frist time job of a amateure. There is incomplete lines and many over runs, the diamonds are of the wrong shape the ratio should be about 3:1.
Interesting..... While I was looking, all of the pictures that I could find of checkered stocks had rubber butt plates instead of plastic. I remembered reading somewhere that the standard stock could have been checkered as a "factory option".