Ethanol in the fuel makes the fuel act like it has higher octane than it really does, compression can go higher with ethanol, the only concern could be fuel system corrosion but in nearly 20 years I have never had an issue running old fuel system components even my experiment with a bunch of parts and pieces in a sealed up peanut butter jar has not shown any degradation of the parts. It needs access to the atmosphere for extended periods of time to absorb moisture and that is what causes corrosion.

As for messaging the pistons I always round off all the sharp edges, you never know when you might get a bad batch of fuel or maybe they are out of premium and you got to run low grade in a pinch or the fuel delivery guy acidently put some diesel fuel in the tank in the ground, maybe you decide later on down the road to put some smaller chamber heads on and the work is already done without disassembling the short block or... it is just cheap/free insurance.