I found your question when I Googled up Royal Krona so my reply may be of little use to you, given that your question dates back well more than a year.
I have a Mats Jonasson piece, Walruses (Walrusi? What is the correct plural?) and I sent off a note to Mats Jonasson (<firstname.lastname@example.org>). Here is my question to them and their reply. I hope it helps you.
And, of course, I'd like to know all I can about this piece. If anyone knows more, I'd appreciate hearing it. Thanks.
(note, I edited my q down to just the basics, their reply is complete.)
I have a relatively large piece (10 1/4" x 6 1/4") by Mats Jonasson.
> It shows 2 walruses. On the bottom it reads RK.3155.M.Jonasson.
Thanks for your email. The product you have was designed by Mats Jonasson when he worked as a designer for another glassworks called Royal Krona (RK) between 1974 and 1978. Therefore, we don't have details re. this product as it has never been part of our collection so unfortunately the only info I can give you is that it is designed by Mats Jonasson some time during 1974 and 1978.
(OK, I did edit out the responder's name)
Mats Jonasson Målerås Sweden