As the 2nd auditions are supposed to be "role specific" they will, presumably, have groups of people who they think can dance come all together, where possible and subject to maximum capacity per session too of course, then various group of potential actors, drummers/percussionists, pointe work ballerinas etc. separate to that.
I would imagine that, if you have not stated/put yourself forward for one of the specialist roles and are therefore being considered as a "general performer" only then you may not hear back as quickly as others as to whether or not you are through to the next stage or not.
I could, of course, be wrong on that but would make some sort of sense from an organizational point and help them keep up to date better as to who they have/haven't seen first and second time around (no mean feat to keep track of accurately from an administrative point of view).
So, say they need 150 to 200 general performer auditionees per session and have a failure/no show rate of 10% or thereabouts, the 2nd audition will have c. 135 people in it, some of whom will not be available on the 2nd audition date (& therefore be automatically eliminated, say a further 10% or so, taking those numbers down to c. 122 people meaning they can offer 2nd audition places to approx 28 to 78 people from the next group that have auditioned first time around, again allowing for 10% failure and no-shows, before they will have reached capacity second time around and so on until all slots are taken and then they will hold off booking up the next 2nd audition session until they've more or less filled up the previous one or even held that one.
I imagine, however, they have split the entire pool of "general performer" applicants into 3 or more sub-groups to start with and are keeping everyone they audition within their respective sub-groups throughout the audition process with the intention of merging all the sub-groups at a later stage when rehearsals begin. Same with the "specalist skill" people (which I guess means that if they rule you out of doing a role using that specialist skill you will only re-join the "general performer" pool of applicants after your 2nd audition is over and they have a better idea of how many places they need to fill at the next available audition to offer you to attend ....... and so on (which may, in essence, mean the specialist performers get to audition 3 times in total rather than 2 of course!).
Rather then doing it than me all the same though - must be quite tedious/stressful to get nearly 100% right !!!
Hope you follow my logic here btw (or have even bothered reading thus far actually !)