Horizontal yellow markings on back of cards?

Hi all, so I was resleeving some cards and noticed yellow markings on the back of one of the cards, which I figured were pen marks of some sort. Then, a few minutes later, I found another card with similar marks of the identical color, with near-identical placement. I did some research and I bought these cards from different sellers more than a month apart. Has anyone else noticed similar marks on the back of cards? Is this an actual print error or are these just pen marks? I assumed they were just pen marks until I found the second card with them. FWIW, both cards are from FRLG (an ex and a reverse holo). Here are pics of the markings from both cards:

If anyone knows anything, please let me know. I can’t find any info online.

I bought a skyridge holo with 2 small green markings on the front, similar to your cards where it seems like a pen mark. I looked up several other of the same card online and found some of them had the same exact tiny markings. So I definitely think it’s most likely a printing error.

Interesting. If anyone else has a Zapdos ex from FRLG and a reverse holo Snorlax from FRLG, check the backs and I’d very curious to see if this is a consistent (or at least common) issue.

EDIT: Holy shit! you’re right! just looked at the scans of a PSA 10 Zapdos ex and it has the same markings! Crazy.

Yep, saw my markings on a psa 10 version of my card as well so either psa missed it or doesn’t care.