Mark, you only need one plant for seed. I only have one plant, and my seeds from this plant has germinated.
They usually germinate the year after sowing.
They have a peculiarity that I have not seen on other Helleborus when they germinate. When the seed germinates and is going up, so is the blade stuck in the seed. All while the stem continues to grow. This has the consequence that the stalk is broken and then it looks like a snail have grazed the blade.
Not everyone in a seed pot but they may be many who do so, and different from year to year.
Some years all work as they should.
I have wondered why, but has no answer.