This reminds me of the wall paper in my sister's kitchen. She used an old timer, well known for excellent work to install the printed paper...he always matched up everything; and was proud (rightfully so) of his work. After a number of years after having the wallpaper installed, my nephew casually commented (between spoons of Cheerios), "Ya, there's a mistake up in the corner"....Everyone was shocked. Later, she ran into the gentleman wall paperer and mentioned it in passing. He was in such disbelief that he had to come and see it for himself.
Some mistakes are so subtle, that they just add character. And that's the story with your quilt.
p.s. It is beautiful. Fixing it is up to you--good luck!