Happened to mine too. I took Sonali's meet outfit off shortly after purchasing her. I placed her shoes in the yellow AG doll armoire and never took them out until last month. Brown discoloration just like you described.
My girls in order of closest bond: Kelsey (6yr old dd) Marisol, Julie, Cécile, McKenna, Sonali, Jess, Lanie, Mattel Samantha, Chrissa, Mia, Nicki, Marie Grace, 4 bitty babies.
Was very excited to receive my trunk 3 days ago until I saw the brass 'American Girl Collection' plate was missing. I called customer service right away and they said the trunk was revised about a year ago and no longer has the brass plaque on the back. Even the hinges are different. It looks easy to break. I wont be keeping this version.
I cant say enough about my Our New baby stroller. It is made of a beautiful sturdy red denim and trimmed with the same gingham taffeta the original bunting, party dress and lullaby basket is made of. The structure is very sturdy and it reclines so doll can take naps. Even has a space in the back to hang the diaper bag. I give this item a strong A+ My daughter's eyes light up when I take it out for her to play with instead of her yellow bitty baby version. I'll allow her maybe an hour per month with it or for special occasions as it is very special and RARE. If you can find one, I highly recommend buying it.