My first gallery submission got roasted for a coffee stain I never saw

Last month I finally put one of my digital pieces in a local show over in Portland, printed on matte paper and everything. I spent maybe 40 bucks on the print and frame, felt great about it. The opening night was fine, couple people nodded at it, no big deal. Then a stranger walked up and asked if the brown smudge in the corner was intentional, like some kind of abstract choice. I looked closer and sure enough, there was a weird blotch right near my signature that I somehow missed on screen for two weeks. Turns out my cat knocked over my coffee mug onto my tablet pen holder and I never cleaned the tip properly. Has anyone else shipped or hung a piece and only caught a flaw once it was in the wild, or am I the only one who needs a magnifying glass before every upload?