My stash has been mating for years. I too, do not remember buying all of those fat quarters or big pieces that I thought I would use for quilt backs. This is just what I have in my sewing room. I have another room in the basement where I have other fabrics such as fleece and flannels. They have also multiplied. I don't even think that the fabrics wait until dark. They just wait until no one is in the room. I have also found batting that I didn't know I have. I went to organize my Civil War fabrics and to my surprise I found that I not only had doubles but four of a kind. I can't imagine that I bought that many of one fabric without remembering that I already had some.