My theory anon is those are levels of classification. Like you have to be above that level to have that knowledge, in the case of 1-99 you need to be level 100.
Just a theory, I meant to dig on it yesterday but I just did a skim on the WP article.
If there's three levels of classified information, but also code word classification and levels of sensitive information, maybe each level has a numerical score to aid in fine grained compartmentalization.
But yeah, dunno. Maybe lurking milfags are able to confirm, or deny, kek.