I have a lot to learn about currency and expected both of these to be mules. Why would one be a mule and the other not? Both have face check #1371 and back check #1015. Thanks!
Quick answer: They both have back plates of 1015 which is above the threshold (930 and higher) so are both Mules, just not stated on holder.
Some background, in the animal kingdom a Mule is a halfbreed between a donkey and a burro. In currency collecting it is a face plate from one series and a backplate from a different series. This happens at the change of a series where the backs look so close that the BEP kept using the old ones with the new front plates until the old back plates wore out and had to be changed.
For example, you have shown notes with a 1935 plain fronts BUT the backs are from the 1935-A series making them both Mules.
Thanks. I suspected it HAD to be a mechanical error but lacked the confidence to declare that. Thanks for clarifying.
Plate positions A and B are from the same sheet, perhaps call PMG and politely remark that the Fr. number is incorrect on their first holder and ask if they would correct it gratis