When it comes to using pastels, I'm a big believer in two things: Removing the labels from pastels that come with them, and breaking up sets so pastels can be stored together in one pallet box. Removing the label allows use of the entire pastel surface, and mixing sets into one central pallet means you don't have to hunt through different sets to find what you need.
Doing both those things does make it hard to identify a pastel if you want to replace a stick. Without a label, you can have a bit of a mystery on your hands, unless you have a color swatch chart to help keep track of the colors.
To make a chart you'll need:
A piece of pastel or drawing paper
Pencil
Ruler
The pastels you want to chart
Make a grid on your paper with enough squares for each pastel in the set. At the top of the paper write the pastel brand and name of the set.
In each grid space note the name or number of the pastel, and a sample of the color.
When you'd like to reorder a pastel, consult the chart to find the matching color. I've found these charts to be really helpful in identifying and reordering my favorite pastels.
Sometimes people wonder if when you have a larger collection with a lot of different brands, it becomes too difficult to identity a pastel. In my experience, by the time you get a large collection of pastels, you also have enough painting experience to know the feel of different brands. I typically have a good guess about the brand of pastel I want to replace, I just need to know the color's name or number.
If my pastels come with labels, I usually remove them while making the color chart. If you'd like a tip on how to remove stubborn pastel labels, check out this post about breaking pastels in half.