Are you saying that these are phones that have built-in polarity guard circuitry, or are they phones to which you have added the PG?
Maybe the phone co installer was confused. He may have understood you to mean that he needed to reverse the wires on BOTH sides of the NID connections. That would essentially negate any reversals. Did you actually watch him do the reversals, or did he just say he did them, and you believed him? I'm not saying he lied to you, just that he may not have understood what he needed to do.
Then, when you did the reversal yourself in the basement, you fixed the problem.
