Making a genetic diagnosis was difficult and blood samples had to be sent away so that results were often weeks and months later. Even then, the diagnosis would come back as a "yes" because a deletion on the 15th chromosome had been found, or "no", because the deletion had not been found. And, as we know today, just because there is no obvious deletion it doesn't mean the diagnosis of PWS is incorrect. A maternal disomy diagnosis (where the developing embryo has picked up two pieces of its mother's chromosome, instead of a bit from its father's) won't show up as a deletion. And certainly the third diagnosis of imprinting, won't show up as a deletion either.
Scientists began to realise there was something more to diagnosis than just looking for a deletion and the breakthrough of different subtypes was made some 15 or more years ago. What does this mean? To the scientists and researchers, it is quite a significant breakthrough genetically. To behavioural specialists, psychiatrists, psychologists and those who manage the behaviours, it is also a significant breakthrough and much work has been done on looking at the three types as individual groups, ie, those with the Deletion (also known as the Type I deletion), those with Maternal Disomy (also known as Type II), and those with the Imprinting. To understand the theory behind all this, have a look at the article by Merlin Butler and Susie Cassidy.
Studies around the world have been done to try to identify different types of behaviour, and characteristics - such as a pretty unique ability to complete jigsaw puzzles (for those with the Deletion), a lighter skin pigmentation (for those with Maternal disomy), similarities with autistic-like behaviours (for the Imprinting), a higher IQ for the Maternal Disomy group (often leading to more challenging behaviours) and many others. But the main thing to realise about all of this is that your child is unique. He, or she, will have many attributes gained from his or her upbringing, siblings, family environment that will make him/her quite different from any other child with, or without PWS.
We know that if it weren't for the scientists, researchers, and medical teams around the world, there would be no gains made in the strides taken to understand the syndrome, but we must also never forget that if it weren't for the parents' concern and love for their child, we would never understand the person behind the label of PWS.