This really applies to any prefinished building material. I have an extra box of each type of flooring in my house, just in case. I also have pictures of the mix ratios for all the paint in the place too (with brand).

As a furniture maker, I also provide my clients with the "recipe" for the finish I use. Usually written somewhere inconspicuous under a tabletop or on the bottom of a drawer. This way if it comes back to me for repair, I know what I used, or if they take it to another shop or do it themselves, they can get as close of a match as possible. A good maker will have no problem sharing this, because they know that their product should outlast them, and if it looks good for a long time, it's a good reflection of their craftsmanship.

The world of "Fast Fashion" has crossed over hard into home improvement, so products are constantly changing and being discontinued, so a few spare up front is way cheaper than a premature redo later on.