This dress is, I believe, a prototype. And the doll on the picture is a Gauntlet Sindy. Probably the gauntlet dolls was sold during 1974 as Lovely Lively Ship Ahoj dolls.
But when Pedigree changed the design of the boxes and packaging in 1975 I think they put the name NEW LOVELY LIVELY on the boxes and changed the dolls to the same doll as the active Sindy sold in 1974, who could only turn her hands and had non bendable ankles. Sadly I have not found any pictures of the 1974 boxed doll.
Since the new Active Sindy Ballerina doll, with more movements then ever, was released in 1975, my guess is that the 1974 Active Sindy had been produced in a large number and by giving her the role as Lovely Lively instead, Pedigree now had two great dolls to sell!