It looks like this. View attachment 5927406
Im afraid it would look like this in the long run if I keep it.
This is not a general yellowing. It's definitely a defect as it is only where the stitching is. I had this issue on a light grey bag as well as a beige/nude bag. I too got store credit, but not enough to buy a brand new bag due to price increase.
I have a white bag, light blue bag, light pink bag, all stored in the same way/area with no issues at all. So, it's clear that the bag is defective. Particularly with the 5 year warranty, you should get a refund for sure.