I've got a crypt cordata, although it is var Grobowski, not Rosanervig.
Grows much like a typical crypt for me... slow to establish, old melt when tank parameters change, normal growth once established. It does take a while to grow to full height, each new leaf slightly larger than the last. I've only grown it low tech.
One leaf in a year does not sound right, do your other crypts grow OK?
Rosanervig is a rare variety that I would love in my collection, it is great for you that you have it!