Broody, I'm so sorry again for your loss. What you shared doesn't bother me, but for those who it does, I wanted to say that it doesn't sound like you had a missed miscarriage at all, as you experienced heavy bleeding/clotting and knew you had lost the baby before you were scanned. And I hope this isn't insensitive, but frankly, I think your sonographer was talking bollocks, as the rate of MMC is meant to be around 2% for all pregnancies, so 40% is scare-mongering by any standards, and anecdotal at best (although I suspect she was probably trying to make you feel better).
It's true that one in four pregnancies does end in miscarriage, but a big portion of these are earlier on, many so early that they are considered chemical pregnancies, which the mum may or may not have even known about yet (I did with my chemical as I had very early symptoms and POAS'd early).
Also, for those who have had early scans, if you have seen a heartbeat at any stage, your chances of miscarriage have gone down significantly. If you see a heartbeat at 8 weeks, you are meant to have a 98 percent chance of a continuing pregnancy.
So please, everyone else try not to worry, as it won't help anything. Your risk of miscarriage is decreasing every day, and chances are if you did miscarry, you would know about it.