Originally Posted by
xliioper
Even though UA website calls these "B" fares, they do not actually appear to be B booking class fares (unless they just book all Economy Plus fares into B booking class) .
The ones I see do book into B, requiring both W and B inventory (e.g. to maintain differential).
The fare type code could be easily used to identify E+ entitlement, but UA could apply another rule as well.