I got an invitation as a Junior and attended this past weekend! (Oct. 16-18) I haven't yet applied for Summer Seminar, as that application opens on January 15.
This is by no means a fact, but amongst those of us who attended CVW, a group of us were talking and decided that we all shared certain characteristics:
• None of us got accepted to STEM.
• Most of us applied late in the process.
• We were geographically dispersed.
That's all that I know, so you'd have to make your own assumption on how the invitation process works for Juniors!