If the FDA audits a company, the company would need to be able to communicate how many labels they have used, how many they have in process that day and how many they have in storage.
As a part of the inventory process it is a requirement to keep a log of labels used.
By having the labels sequentially numbered on the back of the labels is a great aide in helping companies guarantee how many labels were printed per roll and how many are left on that specific roll.
When a company receives rolls from the label supplier they can verify the individual count of each roll and tally total numbers being added to they inventory quite easily by reading the numbers on the backs of the labels.
Serializing labels can also be a good check and balance for that day’s activities to say they started with label number “x” and the roll now shows we have “Y” labels left . It allows a company to see the log sheet, for example, “ I used X-Y labels today so I accounted for everything.”
There is no requirement to have this sequential numbering on the backs of the labels, it is purely up to each company to define the practices they want to adopt for accounting for these labels, the sequential numbering is simply a tool companies can use as a checks and balance process.