You're doing it right
The assessment has put your team in the mostly mature group. This means that you're doing many if not most things the Lean UX way. Congrats! Your customers love you. Is there room for improvement?
If so, maybe revisit the book.
Since you're probably already conducting regular retrospectives on your Lean UX deeds here's a different idea: bring in customers, show them how you work and get some feedback on that.
If you'd like more ideas, subscribe to our 4 issues tips e-mails. Wouldn't do any harm, now would it?