When Nurse Grace is being questioned by Warden Glynn and Doctor Nathan, it is mentioned that she worked at St. Eligius in Boston. This is the hospital also known as St. Elsewhere, which brings Oz into the Tommy Westphal universe.
When Stella is putting books on the bookshelf just before talking to Bob Rebadow, the back of a book can be seen showing Poet's picture. This is very probably his book of poems that Kareem Said helped him publish in an earlier season.