I bought the pink and white full-set that Celeste wears from Fourthborn. She pointed out at the time that there was a small discoloration on the petticoat. I have cheerfully ignored it for something like seven years.
Same story with the pink and white full-set that Adela-to-be-renamed is wearing. I think that it's been in a shoebox in my studio since roughly the time that I bought Honor from Fourthborn.
Since I took the whole day off after appointments for Middlest and me this morning, I got a little ambitious and whipped up an Oxyclean slurry in my largest mixing bowl, dropped in Celeste's big fluffy petticoat (on the left) and Adela's bloomers (middle) and shift (on the right) into it, then lay down for a nap.
When I got up from the nap, I ran a small load in the washer, with Adela's things safely trapped inside a lingerie bag. I'm pleased to report that the mysterious stains are all gone. I have a really cool pressing wand that my sister gave me for subduing the seams on quilt blocks, and it will make short work of tidying up all of those ruffles without melting the crinolines underneath.
(Sometime between now and seven years from now.)