[Mark McLeod]

Stealth mode are events that didn't reach their initial advertised capacity, but reset their open slots to zero, so anyone registering for it would immediately go on the wait list.

There's just no way to see what's going on and when it reached, if it ever did, initial capacity.
Regional Directors do this to give themselves more latitude in assigning limited availability slots.

The Texas Regionals are a good example. They were all frozen below capacity, so preferential treatment can be given the Texas teams. They have a State funding restriction that says the teams must play in-state or not receive the funding.
Washington State has a similar State funding restriction, but they handled it up front by freezing the team list right from the start, then they opened it up when they knew all the State teams could be covered.