From the recruiting department regarding the 'top tier' emails.
'Everyone that receives an application review gets a letter to inform them of their status. There are quite a lot of applications being reviewed. Unfortunately it is not a first in first out process as there are many factors to be considered. I tell everyone, it's great that you are competitive and have been advised so that you can start preparing for your interview, so just be patient and we will get to your invitation as soon as possible.'
Big hint in there. Don't wait for the invite to start prepping. Prep for the Cut-E, too. Top tier means it's coming.