I am one of the doubters. The Underground Railroad definitely happened, and there were definitely quilts made during that time in history, but the rest is fairy tale. Think about it... how would you ever get the word out to the escaping slaves or their helpers, of what quilts to look for? How could anyone truly rely on such a system with their lives? It's a nice fairy tale, but a fairy tale nonetheless.
Same for those fisherman's sweaters... the story being that the fishermen knit patterns into their sweaters, designating what towns they came from lest their drowned bodies ever wash ashore in a faraway place. This has been debunked as the invention of companies who wanted to sell their sweater patterns, to create in them more interest and romance.