I ordered a replacement lid for the Samantha I purchased at Costco. It arrived.
It arrives in the same box a doll would arrive in. This is nice, if you wanted to store the doll and box in a cardboard box.
This is the Box Samantha was in, inside the Costco packaging. Here is a comparison to an American Girl box bottom. The American Girl box bottom is a little deeper and longer. I didn’t know this at the time I ordered, because I could have ordered a replacement box bottom. But the replacement lid does fit, just not as tight. I can add a few pieces of cardboard to the end of the length of the box bottom to get a tighter fit.