There doesn't seem to be a relevant chief counsel's opinion on the FAA website. Considering the following though, I think I will continue to clarify that I have received a "clearance" into/through Class B, prior to entry, anytime I'm VFR (or shortly expected to be) unless I hear something to the effect of "cleared into Bravo". Controllers often voluntarily say this prior to being asked, so that must mean something. A heading and altitude assignment alone do not seem to make a "clearance".
From the AIM:
4-4-3 Clearance Items
ATC clearances normally contain the following:
a. Clearance Limit. The traffic clearance issued prior to departure will normally authorize flight to the airport of intended landing. Under certain conditions at some locations...a clearance is issued to a fix within or just outside of the terminal area...
b. Departure Procedure....
c. Route of Flight....
d. Altitude Data....
e. Holding Instructions....
From the P/C Glossary:
AIR TRAFFIC CLEARANCE. An authorization by air traffic control for the purpose of preventing collision between known aircraft, for an aircraft to proceed under specified traffic conditions within controlled airspace....Pilots may also request clarification or amendment, as appropriate, any time a clearance is not fully understood...THE PILOT IS RESPONSIBLE TO REQUEST AN AMENDED CLEARANCE if ATC issues a clearance that would cause a pilot to deviate from a rule or regulation...
P/C Glossary again:
ATC INSTRUCTIONS. Directives issued by air traffic control for the purpose of requiring a pilot to take specific actions; e.g., "Turn left heading two five zero,"...