Interesting. I was going to ask whether you were sure the designer was Landberg and not Palmquist, but the numbers on the bottom are the correct numbers for Landberg. My question stemmed from the fact that I've a small light blue sommerso vase with the exactly same ship engraved on it, also an Expo piece, marked Orrefors Expo PU 37 -55, designed by Palmquist a year earlier. Was it common for different designers to use exactly the same image? I've attached a picture of my piece. Apologies for the quality but it's a little late here in the far West.
My understanding of Expo is it was "art glass" produced outside the usual factory run. Each designer was given his own number series, which also identified the year. The pieces weren't necessarily shown at an exhibition.