What are the "flexi-ranks" (Lambda, Mu and Nu)?

In the Statistics, the Adult rank spots are out of 12 but there are 3 extra ranks that don't show up on the Ranks page. (lambda, mu & nu) So does that mean if a pack is 12/12 for adults there is still space left?

Pretty sure I can answer this! If a pack has 12 wolves but only 1 wolf in the higher tier, they would need those three extra spots to make up for it. (: So the ranks would jump from Alpha to Gamma, but there would be 3 extra ranks (lambda, mu, and nu) so the final three wolves have ranks.  Hope that makes sense!