Patterns for Samantha Parkington

Samantha is of course very close to Rebecca's period. Samantha is living in 1904, and Rebecca is living in 1914.

Samantha belongs to the Edwardian period, which is from 1901-1910. Nonetheless, Samantha is often described as being Victorian, and Rebecca is often described as Edwardian. Neither of these is correct!

So deciding which pattern belongs to which doll may require some research.
However, if it is sleeveless, you can rule it out for Samantha. Grandmary wouldn't let her wear it.

A few patterns work for either doll. This includes:

Anne Van Doren Designs Edwardian Style Dress and Apron

Anne Van Doren Designs Victorian Style Underwear

Dollhouse Designs Victorian Underwear

Genniewren Designs Harriet Dess

Jen Wrenne FREE Sailor Dress Pattern

Keepers Dolly Duds Reefer Jacket and Hat

Keeper's Dolly Duds Simplicity 1179 Vintage Inspired Clothes

Bunny Bear's 1900 Sailor Dress Pattern

Thimbles and Acorns A Piece of History Dress

If a pattern specifically has a date on it that is 1910 or later, Samantha probably shouldn't wear it.

These patterns are specifically for Samantha:

Dolls at Hearts Designs Edwardian Day Dress

Dolls at Heart Edwardian Tucks and Lace Dress

Farmcookies Welcome Back Samantha

Flossie Potter Central Park 1904

Flossie Potter Duster Driving Set

Heritage Doll Fashions Samantha's Ice Cream Dress

Keepers Dolly Duds Victorian Christmas Caroler

Lincoln Mold 1904 Bathing Suit that fits American Girls Dolls

Lincoln Mold 1904 Undergarments that fits American Girl Dolls

Lincoln Mold 1904 Girls Coat and Hat that fits American Girls Dolls

Lincoln Mold 1904 Dress that fits American Girl Dolls Patterns 40, 41 and 42

Pleasant Company Samantha Patterns at AG Playthings

Wren*Feathers Edwardian Heirloom Pattern Set

Grandmary was so strict that Samantha could be wearing all or part of the Thimbles and Acorns Victorian Unmentionables as well.

Elsewhere on the web:

Fancy Frocks 1904 Sailor Dress

Fancy Frocks 1905 Sam's Winter Frock

Samantha's Cross Stitch:
Hodgery Podgery 1900s Style Historical Sampler

Okay, that's a short list.

Inspiration for further Samantha dresses can be found at The Bleu Door. This shows dress patterns produces for Bluette dolls, and you can search by year and decade. The earliest year is 1905, which is admittedly a year late, but still very close to Samantha's period. If you assume she got the dress after Christmas, it works just fine.