Post processing:
The post processing stage of NN is where almost all useful information about a particular release is generated, however for the sake of simplicity I will only be discussing the "Additional PostProcessing" stage, which by default will say "PostPrc : Performing additional post processing on last x releases" Lookups and nfo processing are handled in a different part of the post processing.
This stage by default is limited to 100 releases processed per run of update_releases, and handles deep rar inspection (including password checking and rar contents) as well as the generation of mediainfo and ffmpeg previews.
This limit can be increased, but it will increase the time that update_releases takes to run, and may delay grabbing of new releases more than you like.