The main designer at Flygsfors in the 1950s was Paul Kedelv (1949-1956)
As you will probably know he designed the 'Coquille' range - this was so popular that it continued to be made with the etched marks for years after, I have bowls from the range dated into the 1960s.
So where does this put the 'Flamingo' range - with etched marks of 1960 to bases it was obviously made at the same time as 'Coquille' - however working on the basis that I have never seen a piece of 'Flamingo' dated within the time period Kedelv worked at Flygsfors, I don't think it was designed by him.
Wiktor Berndt (1955-1974) was the main designer at Flygsfors after Kedelv - he is well known for his 'Primitive' series but could well be the man we are looking for reference design of the 'Flamingo' range, I believe he designed his socks of at Flygsfors and was there for a longer period than Kedelv.
Also there is a similarity in some of the 'Flamingo' designs to 'Coquille' this would make sense as the range was conceived perhaps only a year or two after Kedelv left and it would have been a transitional period.
These are just my ideas - can anyone with the following books give more information or recommend a book with extensive info on Flygsfors for this collector.
Scandinavian Glass 1930-2000: Fire & Sea
Leslie Pina & Lorenzo Vigier
Scandinavian Glass: Creative Energies
by William L. Geary
Scandinavian Glass, 1930-2000: Smoke & Ice
Leslie A. Pina, Lorenzo Vigier
20th Century Factory Glass
by Lesley Jackson
I note that Flygsfors Flamingo is hot stuff on eBay and in auction rooms at the moment - with so little known about how extensive the range was and how long it ran for prices seem high (that rush of blood to the head) but set to go a lot higher - it is very beautiful after all.