The stock drive is 500GB.
323GB free + 84GB games + 100MB other = 408GB.
Applications is only the three games. Nothing else installed/deletable.
As others have pointed out, 500GB is a marketing number. The OS sees GB (and MB, KB) in chunks of 1024 compared to a straight 1000 multiplier. e.g. 1GB = 1024MB, not 1000MB as marketing reports.
Thus, 500GB /(1.024^3) = 465 "real" GB.
1.024 is the ratio factor which is cubed because it's used three times: Bytes in KB (1024 vs 1000), KB in MB (1024 vs 1000), and MB in GB (1024 vs 1000).
That means 465 - 408GB leaves 57GB reserved on the drive. Not all of that may necessarily be occupied. There is likely a swap partition, the OS, reserved space for game clip sharing, etc.
Not that it's a big deal at all (408GB is more than enough to begin with, plus you can always expand storage), but I remember how cows made a big deal about how the space available with the Wii U was not as much as advertised. I wonder if we'll see them call Sony out on the same issue now, or if we'll see their legendary hypocrisy in full force again.