The problem is the known world of perennial kale is just way smaller than what it really is, because while everyone tries to cram through the overly tiny front door of Daubenton’s (and ‘kosmic’), the broad back door of perennial kale from seed remains unknown.
I don’t mean seed harvested from perennial kale, which is more or less an uncommon happening; and good luck getting it. I mean seed from certain kinds of biennial kale who’s genetics teeter on the border of perennial and biennial. With these, it can be as much of a fifty fifty chance each plant will be perennial.
That is only for select cultivars such as ‘Pentland Briggs, ‘ ‘Western Front, ‘Sutherland.’ I’ll do some more research this year with some other varieties rumoured to have the elusive talent of immortality. So, in about two years, I’ll let you know the results. Until then, if you are in a dire straight to gain eternal kale, I would recommend you set an area aside for a lot of kale, and try the varieties mentioned as an alternative, roundabout way of getting it.