When one strip fails the set still powers on but the picture is dark in a band, dim overall, or visible only with a flashlight held to the screen.
Strips are matched by the strip part number and by the model they were built for. A set can use several different strip revisions across production runs, so compare the number printed on the strip itself, and count the LEDs and the strip length, before ordering. Sets that have lost one strip usually need the whole set replaced.
Kits here are sold as full sets where the original was sold that way. Ships from US stock with tracking.