This is the confusing part. The old site was a wordpress.org installation on GoDaddy hosting. It was my only blog registered on wordpress.com - I don't fully understand that relationship, but it was. When I logged in to wordpress.com and tried to "Edit My Profile" it was linked to the old wordpress.org site which no longer exists, so wordpress.com definitely had record of that blog.
And, I'm asking because I thought I would use that blog shortname on wordpress.com since I 'owned' that blog shortname before. I'm confused why a "reserved" blog name is not usable by the person who reserved it, and what effect there might be because the blog name referred to a wordpress.org site.
I wonder if I originally created that blog as a wordpress.com site and then moved to the wordpress.org install because of the custom template I was using? Still, I don't remember going to wordpress.com and deleting that blog. Perhaps I did?