A few years ago, I was in a wedding that was about a 6 hour drive away. Anyhow, the bride ordered all the bridesmaid dresses through the shop where she got her dress. We all came down for a first fitting about 3 months or so before the wedding (alterations were included in the price of the dresses). Because most of us lived rather far away, we couldn't make it for another fitting until the day before the wedding.
My dress didn't need many alterations. It was way too long, but other than that, it pretty much fit perfectly. One of the other bridesmaids (M) had been losing weight, and her dress was absolutely huge on her and needed tons of alterations.
Fast forward to the day before the wedding. M and I go to the shop to try on our dresses. Hers looked like it hadn't even been altered, and she was swimming in it. She'd lost a little more weight since the first fitting, but not much. My dress on the other hand had inexplicably been taken in and I couldn't even pull it all the way down over my hips!
For the life of me, I don't know how that happened. I mean, they pinned the dresses to mark what alterations needed to be done. It doesn't make sense. Thankfully, they were able to let my dress back out and alter M's in time.