When I was growing up in the sixties and the seventies, all the Barbies were the same size. There was no confusion on which outfits would fit, or what "type" of Barbie a person had. All the standard Barbies had the same shape and they all shared clothes that fit.
After I started designing Barbie clothes, I noticed that some of the newer Barbies I had purchased weren't looking so hot in the outfits that I had designed when using a vintage doll for a fitting. Shirts were either too tight or loose, or worse, a strapless dress would slip off the slimmer more modern doll.
Another issue was the texture of the dolls. Some of the vintage dolls had the rubbery legs while the newer versions were sleek and smooth and clothes would glide on and off like butter. Which wasn't a bad thing, but if I was using that newer model to tailor an outfit, I would later struggle to "slide" the outfit on a vintage.
All these were major issues when trying to design and sell clothes to the public. WHICH doll was my customer trying to fit? Even though this outfit looked great on my newest model, was my customer purchasing this for a vintage?