There is some clarification from Mena at Six Apart today. Here is my question on multiple author limits answered:

What if I have a weblog or author who’s no longer active on my installation?

This was a less common question, but it’s one that I think we need to clarify.

The limits in the license govern the use of Active weblogs and authors. For the purposes of the license restrictions, we’re defining a weblog as “Active” if you’ve posted to it within the last 90 days (receiving comments do not count), and an author as “Active” if that author has posted within the last 90 days.

So, if you have a couple of weblogs in Movable Type that you no longer post to, but want to keep around for archival purposes, that doesn’t count towards your license limit. The same goes for authors on your installation.

This means I can have guests host my blogs and won’t violate the license.

I feel better.