It sounds like you have the problem in hand. Sorry to be late to the party, but I can offer a possible explanation to the relatively sudden onset of low voltage problems.
I was asked by our local church to figure out why, suddenly, the lights would flicker when the A-C units kicked in. I took measurements and determined that the line voltage on both 120 volt legs would sag 5 volts when the compressors started. That is more than the recommended maximum 3% voltage drop that we go by.
It seems that the lighting company had re-run and re-directed our aerial drop wire from an adjacent pole-mounted transformer, to one about 4 sections (~600') away.
They had done this because a commercial building across the street had complained of low voltage, so the brains at LIPA (motto "We're even worse than the phone company") moved the church to a different transformer, and in doing so added more copper, which results in more resistance, which results in more sag.
I convinced them to put things back the way they were, and to move the commercial building's service to a transformer one section back. Now everyone is happy.
Something like this might have happened in your neighborhood back in May.
