The plaid (pronounced "played" --a large piece of woolen material woven in a tartan pattern, although it was probably shades of gray originally) was an old textile concept for Highland wear.
When wrapped around your body in a certain way, it became the breacan faile. At Culloden, the sprig (our sprig would have been cotton grass) worn in the bonnet was the item which identified the clan relationships, not the highland dress or the woollen cloth woven in a specific design.
And what tartan would you wear? When the 1746 proscription on wearing of Highland Dress and the Tartan was lifted around 1814, it was done so for many reasons not the least of which was economic. The individual most responsible for the change was Sir Walter Scott. He was assisted by various actions by King George IV, Prince Albert, and more recent members of the House of Windsor. I recently saw a TV interview showing Prince Charles in his kilt romping in the woods with his sons. The textile manufacturers (my Scottish source would call them "drapers") were exploiting a new marketing strategy when they began the process of tying specific setts to specific families.
In the case of Henderson, the sett was named because the most available and influential Hendersons around Edinburgh were from Fordell. Also, they had a coat of arms et al, unlike the other choices. Some of this comment is conjecture but it makes a lot of sense.
-- by Russ Henderson