I have had very good luck with moving hellebores around, even thought I did read that they don't like to be moved. You probably got all of the roots for them.
I have no dark hellebores at all. I'd like to see pictures of yours when they come up though.
Mary

Best time to move/divide them is as the flowers are going over and the new foliage is just getting underway. Big plants can take some shifting, but get as much of the root system up as you can. Wash all the roots off and split into big pieces being very careful with the new white roots. The old black ones don't matter so much, but don't let the roots dry out!!.

Just shop around for the black ones in the spring, do you have Hellebore nurseries near you? Get there in Feb/March and buy the best you can in flower. We're lucky here in Britain as we have several specialist nurseries, where you can get black singles, small and large flowered, anemone centered and full doubles, can be up to $40 for the best. Of course you could try mailorder.

Cheers Greenmanplants