First time I ever attempted this, actually, but I wanted to insert some information between the list items in an ordered list and pick up the numbering where I left off. The problem, however, is that WordPress strips out the "start" attribute on the ol tag, so this doesn't appear to be possible.
Now, I know that this attribute was deprecated (for some bizarre reason I never understood) in HTML 4.01, but in HTML 5, it's back. So I humbly suggest WordPress leave this attribute alone when it finds it.
For reference, I'm blogging on my university's installation of WordPress Mu.