My dates only varied by a day with DD1, so I went with the one in the middle of the 3.
With DD2 & DS they measured 4 days ahead, but I still went with the original LMP dates. DD1 went from the 29th to the 25th. She didn't come til the 5th of the next month!
This time I have gotten the same date at both the 8 week & 20 week scans. All I know is that my bub will come when its ready. The date means nothing to me anymore. Just early October, thats what I tell everyone
I do have a friend on FB who was the same as me, but she moved to 2 weeks before me, then somehow she's another week further, putting her 3 weeks further all up. I don't know how it keeps changing so dramatically