Why would there be a siginfigant numebr of returned 4-day with preview returned during or just after the main sale?
The assumption is that there are a lot less PN badges sold and stickers allowing access are given out to returning volunteers among other groups so they can always create more of those badges.
Judging by how much more crowded it's been the last 2 years, they've really increased the # of people they let in on PN.