In our case, a prototype is a tester made at Pendleton's Pacific Northwest mills when new designs are in the works. The prototype may be very similar to the blanket that ends up in the regular retail line -- or it may be very different! Sometimes, prototypes are made to compare different finishes (like flat vs. napped, or felt binding vs. whipstitching). Sometimes, prototypes have slight variations in color... and sometimes, they have dramatic variations in color from the final version you see in the Pendleton catalog.
The blue blanket on the left is a prototype Vintage blanket. The red blanket on the right is the Vintage Ganado Blanket currently available from Pendleton. The design is the very similar, but the colorway changed dramatically from tester to finished product. (We have both blankets here at the Woolen Mill Store, if you'd like to see them in person!)
We often have a selection of prototype blankets in robe (64x80) and queen (90x90) sizes at the Woolen Mill Store. Visit us at 8500 SE McLoughlin Blvd. in Portland, Oregon to see what we have! Prototypes are only available in very limited numbers.