We always try to freeze separately, one in the straw. We usually transfer on day 5, so we freeze blastocyst, now we always freeze one.
Sometimes we indeed defreeze embryos which were frozen six years ago, and in that time we froze them in the same straw. We defreeze the embryos, and if we just transfer one, we freeze the other one, there’s no difference once again in the results, even with freezing them two times. So if you have two embryos in the same straw, and you want to transfer just one, you don’t have to worry.