Branches and all commits

Should *all* commits be reachable via at least one branch? I ran into a 
situation this weekend that has me a little confused. I had performed a 
number of commits and such and I noticed that the author and committer 
info had suboptimal values. A bit of searching led me to a comment made 
by Linus that basically said "go hack git-convert-objects", which I did. 
After performing git-convert-objects on every commit object in 
.git/refs/heads and the requisite pruning, etc... just about everything 
looked fine. However, I still had a long series of commits that 
contained the wrong information. Further inspection makes it appear as 
though these commits are not reachable via any branch, although they are 
/all/ reachable via a series of tags. I worked around the problem by 
further modifying git-convert-objects to also understand tags (at least 
the basic ones I've got) and that's all taken care of, but the question 
remains: should *all* commit objects be reachable by at least one 
branch?

--
Jon Nelson [off-list ref]