Due date change. :(

Anyone’s due date change quite a bit after first apt? Originally, my due date (based on LMP given to me by midwives over the phone a few weeks ago) was January 22. At my first apt the other day, it was changed (based on ultrasound- which I get is more accurate) to January 31. And technically is was really feb 1 but they would have to change a lot in their books and see if I even was able to stay with midwives if it was a new month (since there can only be a certain number of women due the same month). That seems like a huge jump to me.