When IFR aircraft are vectored outside of Class B airspace, you need to advise them. It is very common when a final gets extended during heavy arrival traffic. It happens at BWI as well, especially on a west operation. I will try to find the .65 reference on this.
7-9-3. METHODS
a. To the extent practical, clear large turbine engine-powered airplanes to/from the primary airport using altitudes and routes that avoid VFR corridors and airspace below the Class B airspace floor where VFR aircraft are operating.
NOTE-
Pilots operating in accordance with VFR are expected to advise ATC if compliance with assigned altitudes, headings, or routes will cause violation of any part of the CFR.
b. Vector aircraft to remain in Class B airspace after entry. Inform the aircraft when leaving and reentering Class B airspace if it becomes necessary to extend the flight path outside Class B airspace for spacing.