I am not going to really worry about an official CD1 until AF actually comes. I have been toying with waiting on AF before trying again, but it is taking a month for this m/c to finally come to a close (my HCG was at 78 on wednesday down from 300 the previous week) ... so I think once my #'s hit zero we are going to start trying immediately..
We're planning on waiting TTC until the New Year as I have a minor operation at the end of December and I was told they don't do it on pregnant ladies until they're at least 14 weeks. I basically want to know CD1 so I can try and guess how much longer the bleeding will go. With my first loss I bled for about 10 days and AF came on CD26.
I think I'll go with the day I passed the baby as CD1. Makes the most sense to me. Bleeding picked up a bit today so I guess still got a whiles to wait for it to stop.