In olden days, when Match ammunition was ordered, the number of rounds (lot) to be produced was specified. A lot can be only a few rounds, say 20,000 for a specific purpose or competition, or as many as a million or more. Each cartridge in a lot is manufactured to the same specifications. During manufacture, constant testing is done to insure quality. Some lots may be tested several times a day. (It would not be good if a million rounds were produced without testing only to find out that something went wrong after the first 50,000.) Records are kept and the finished lot can be divided into sub-lots based on accuracy. For example, sub-lot A may be boxed for slow fire, sub-lot B packed in clips for rapid fire, and sub-lot C packed in cartons and clips for practice.
Bullets to be used in Match ammunition may be graded on a curve and divided into groups based on their accuracy and intended use.
Up until 1967 or so, certain lots underwent extra attention to detail and testing, using only the best bullets available, and even having special powder charging plates set aside for them. That lot was designated for the National Trophy Matches at Camp Perry. A special headstamp was used and the boxes were specially marked.
That was then. As the quality of components became more consistent, the lots were produced to a certain accuracy standard and not didvided into sub-lots. Certain groups that did not test well could be set aside for practice and you’ll often see boxes marked as such. Production of National Match ammunition stopped in 1996. Most shooters now use handloads, commercial ammunition, or the Long Range sniper/match/tactical rounds made at Lake City.
Whew. I’ll bet that’s more than you wanted to know. I could have written an entire article on this.