Every school will have their own workflow including differing procedures/standards for II, who may be authorized to decide that, and how applications are reviewed and evaluated. For example, a school's adcom may set some criteria prior for "high level" or "outstanding" candidates and the adcom director has authority for II to these. Some may have long time admissions director, active associate dean, etc, who will pull files of what they consider a worthwhile candidate. Some may split up applications into subcommittees or individual readers who find something worthwhile and arrange an invite. Others may have stricter protocols. So there are multiple steps and people reviewing applications. It isnt one monolithic "review." In my experience, most schools dont offer significant number of invites until the entire file is complete. That is not necessarily complete from everything you have listed, but complete from their perspective which could be 1 committee letter or 3 individual letters. Some may not consider it complete until all the letters you have listed are. In short, everything prior to a full/final vote of acceptance, rejection, and waitlist, does not necessarily have everything in your file. Trying to discern a pattern that may be different for different individuals and different schools is a waste of time, energy and effort and does nothing but increase paranoia around Fear, Uncertainty, and Doubt, the dreaded FUD factor.
