looking back at old test... HELP

Okay so I was getting ready for bed and just for some reason looked in my trash can at some of my old test and a couple of them have faint lines that I didn't notice before?!? Could this just happen after being in the trash for too long? Or does this mean I didn't wait long enough to check it? The one from this morning is still negative these are from other days within the past week. HELP