Fren, there are two native North American Yellow Ladyslipper Orchids. Cypripedium calceolus (Yellow Lady Slipper) and Cypripedium calceolus parviflorum. For reference I have attached two thums illustrating each:
![](http://www.orchidboard.com/community/gallery/data/666/thumbs/d12890s.jpg)
Cypripedium calceolus
![](http://www.orchidboard.com/community/gallery/data/666/thumbs/d12989s.jpg)
Cypripedium calceolus parviflorum
As you can tell, there is not a lot of difference between the two other than the Small Yellow Lady Slipper is (obviously) smaller and grows under differing conditions. I checked C. parviflorum and it is syn. with C. calceolus parviflorum. My feeling is the vendor
may be correct as well as you are probably correct.