For example with the more expensive hair that is reusable, place a colored rubber band along with track weft upon removal. Record the placement and band color on a grid so that you can replace the track in the same order and area as the original style.
The extension hair can shampooed and conditioned with the bands along the weft of the extension leaving the rest of the hair strands unconfined to rinse freely.
Need more than six colors? Use two or three colors as another way to get additioning color coding options. Ultratress extensions and other reusable extensions can be tedious to keep up with small strips. The colored bands can be used to probably keep track of about 18 pieces at a time. Maybe get your client to assist with writing the information down where each piece belongs based on its color coded band.
Nine different colored rubber bands pictured above: brown, yellow, navy, pink, white, purple, green, red, and light blue.