There are many different kinds of rhizomes. Iris and Trilliums have rhizomes, too. However it's very unlikely that your seedlings, wickedelph, would develop them. This is what Jack Frost leaves look like. Notice the big difference in the shape of the leaf, especially where the blade meets the leaf stem, and the difference in vein pattern, compared to your suspect plants. Reversions do occur, but what changes is the coloring, not the other characteristics. So it is not a Brunnera.
Something that's been confusing me: you say the leaves are fuzzy, but in all the pics they look shiny and smooth, and both front and backs don't look hairy at all (??????).
Brunnera is very rough-fuzzy, not at all like your pics, either.
