Ashley, I have several clones of H.niger, and there are differences in them. Some are clearly more short-lived than others, and there are also differences in their time of flowering. The first start in December (and get damaged by the winter here, but they may be very good plants in warmer climates, and prolong Helleborus season), and the latest one always starts to flower in late April. I have grown it now for ten years, and it is always late, no matter where I plant it.
One of the best is H.niger which I have grown from Holubeck seeds (from Italy). It starts to flower in April as soon as snow melts (it may flower earlier in warmer climates, but it is cold hardy also here), and always flowers well and grows well. Also it has red tips in carpels (the other clones I have have green tips) which makes it look a little different. It always produces plenty of seeds, and if you want, I can send them to you next summer:).