I got these stamps in a lot, and I noticed they appear to have expertizing marks on the back.
I assume that is because they appear to be Sc. 49-51 (no watermark and appears to be thin (pelure I guess?) paper) with a 2017 Classic Specialized Catalogue value of $9.5, $9.5, and $21.
Does anyone know who the expertizing mark is for? I tried doing some research, but have been unable to find it so far. It looks like the mark says "FJ.", but there isn't a bar on the top of the "J"....