"A total of 75 children, approximately age six and selected for their specific genetic dispositions (that is, being as close to perfect as science could determine), were "recruited". They were replaced with congenitally defective flash-clones to cover the enlistment, and trained, primarily on and below the surface of Reach, by one Chief Petty Officer Mendez, arguably the best Drill Instructor in the Navy. Their family names, whatever they may have been, were stripped, purged from record, and forever replaced with a 3 digit designation. Their upbringing would be defined not only by gruelling physical routine, but by a comprehensive academic tutelage under Deja, a Class II AI created specifically for the SPARTAN II project."
Nothing says that these were in any numeric order, only that 75 were selected and given 3 digit call signs