Regulations are actually written by the government agencies responsible for the subject matter of the laws. Legal dictionaries refer to docket numbers in the very limited context of cases to be heard by a court. The origins of the term, docket , are unknown. The term docket has several meanings. This last use, by the way, is the least legally precise definition of the term.
Legal dictionaries provide the first three preferred definitions.
A docket number is simpler to use than the entire title of a case and less confusing - an attorney's clients could have multiple proceedings or case files with very similar labels. It is also easier to search for a short number than for a long title of a case file. There is a greater chance of an exact match on a simple number than there is for an exact match on a title when searching for it. By the way, you don't have to be an attorney to have a docket number . Anyone can have their own docket number to help distinguish among their applications - just keep them simple and use a consistent numbering scheme.