@banjocats - the stats page only shows a list of followers who have subscribed to read your blog via the wordpress feed page. ('read blogs' page found via a tab on the home page when logged in).
@banjocats and @robertholloway:
You'll be able to see who has access to your blog (but not their roles) by going to Settings on your dashboard then clicking on 'Privacy'.
On your dashboard, if you go to Users, then click in 'Invite New', then put the person's username or email address in the space provided and then click the 'role' drop down and choose the other role you want for them, then just send a new invite - it won't overrive the old one, as far as I know and you don't have to delete their past invitation - that should do the trick.
However, in case that doesn't work, I've marked this topic with 'modlook' so that staff or a moderator will look at it. I have couple of private blogs myself and I know that sometimes there are problems with them that are not as easy to solve as with public-access blogs here. And I also don't see anyone other than myself on the 'all users' page. I suspect that people who start off as viewers (readers), don't appear there anyway - it's probably for changing a status down rather than up, but I can't be sure.
By the way, you should know that the support pages for anything here on WordPress have extra links to related support pages and that is why I gave the link in my comment above. Not only does it give basic info that you might already know, but it also gives info that you might NOT know. And these topics here in the forum are for the use of all who blog on WordPress.com some of whom might have less knowledge than you.
Also, in case you don't already know this - nearly everyone who gives answers on the forums here are volunteers, so you have to wait til someone is here who actually knows the answers to your questions and it might not be instant.
Be patient. If my response hasn't helped, then just hang in there and someone will - hopefully - be along soon who can.