Edit - I have just been informed they were, while still on the sheet, sat in the sun, so it looks as tho sun fading has occurred through the front of the card but only over the areas that were light on the front, hence the text showing through to the back 
Apologies to anyone who may have took time out of their day to look this up 
Hello! I have recently come across some Bandai Carddass Minis - These were peelable from the back of jumbo anime style cards.
Quite a few in the lot we purchased had what I initially thought was sunfade but upon closer inspection I can see on a handful they have the words & images printed onto them that were on the other side of the sheet. I have took a photo that can be seen below of the Mew and Mewtwo as it was very obvious on these cards in particular.
So of course I took to the internet to try and find some information, if this is a common occurrence maybe that I just hadn’t happened to find before, but I couldn’t see anything on the topic. Is anyone familiar? Could it be an error during printing? I was quite excited when I realised this was a possibly as I collect error cards so this would be a fantastic addition to my collection & something I would hope to try and grade with CGC at some point - let me know your thoughts 
For the record we know the person they were bought off, he’s a friend of ours and has been collecting since the beginning, he peeled them personally a long time ago and likely didn’t even take it in at the time, I’ll be excited to share this feedback with him also
I am not sure what sheet these come off so just used this one I had about as an example, you can see the text in the top corner is what I’m referring to as being printed onto the mini.
I have also snapped a screenshot from eBay of the same Mew but how it should look, posted below (Not my photo)
