what does the "series" mean next to your score?

[Bikini Princess]

If you look at your score on your AMCAS online application, it has a Series # next to it..mine is 23. Any ideas on what this number means or refers to??

 

[RT]

08/00: 20
04/01: 21
08/01: 22
04/02: 23
08/02: 24

RT

 

[la9s]

It's the number of MCAT examinations offered since the institution of the new exam in 1991.