Yes, it is certainly possible, as the bulk proteins are what is acting as a blocking agent, with some protein degradation that does not affect the blocking efficacy. The other issue is was the tube ever opened? If it was, check for obvious signs of bacterial proliferation i.e. opaque solution if the solution is still transparent run it through the 0.22 um pore filter ether syringe or vacuum-driven this will eliminate any bacteria or protein aggregates that might have formed in the solution.