Newbie Instructional Design Question

Our team is about to design our first curriculum after taking the "Instructional Design for e-Learning" course.  We're currently working with the SME to determine what content we need to teach and how to organize it.  I would like to prioritize our content into could know, should know, and must know, as recommended by Wiggins and McTighe (see attached), but I'm not sure what to do with the "should know" content. 

I know the "must know" content should be taught and emphasized, the "could know" content should be optional (or even a link to an external source), but what do we do with the "should know" content?  Does it need to be taught, but not emphasized as strongly as the "must know" key concepts?  One of our team members even interpreted "should know" as the learners should already know this content, so we don't need to teach it.  I'm not sure that's correct, but I wanted to run it by the E-Learning Heroes hive mind. 

I appreciate any advice and feedback.

Thanks,

--Darby