Testing

Ok, so I am just curious what you ladies may have experienced. So I know that after you take a pregnancy test once your past the max time it's now invalid. With my experience if I get a negative even if I go back and look at it it's still negative maybe even stronger negative, but this last test I took it was not as strong of a negative as I am used to seeing and just out of curiosity I went back and looked like I always do even though I know it's not valid anymore and for the first time ever it was positive, I know it does not count and I still be re testing in a few days, but has this happened to any of you and you were pregnant or not I am just wondering what other experiences you ladies have had. Sorry for the long post im just in a curious mood.