Ally, I used to freeze and thaw cells (but not embryos) and the process would kill some cells, but not all, so if you froze 10 cells and 7 survived, then those 7 would multiply and go on and do their thing so you'd have a nice sheet of muscle/skin/eyeball/knee/whatever grown up in the lab. The zygote frozen down may have lost some cells, but that's OK because others lived and can continue dividing. Cell fate/cell mapping doesn't occur until later in humans (so you can lose some cells from a zygote and still get a healthy, perfect baby) so any cell division means that there are some alive cells, so it all sounds great to me! As I said, I have never worked with embryos, but I'd be well chuffed if that had happened to the cells I had frozen and brought back, especially after a two-year-plus freeze.

Roll on the 3rd of October!