emit:From what I understand a 7-day cut-off should be impossible!
Sperm just aren't supposed to be able to live that long. So either there is some variablity in the accuracy in the ultrasound or your DH has miraculous sperm. I know nothing about charting, so I wil leave that to someone else! 
that was my thought as well, heck, 5 days is pushing it really and I had very little CM so survivability should have been pretty much nil. My chart also doesn’t look like I could have O’d later… but it is possible that she didn’t implant as schedule, or and this is what I’m hoping for… it’s another little girl! My dd was teeny tiny at birth and measured way behind on the 16wk U/S.