By definition (and common usage of the language) a phone with a polarity guard "guards" against wrong polarity. There would be no reason to "guard" against correct polarity.
So, older phones, made during the period when the phone company charged extra for DTMF service, did not guard against reversed polarity, for a financial reason. TPC could (and did) reverse line polarity at the MDF when they discovered a subscriber "illegally" using tones to dial out.
Later, when DTMF service became "free" there was no reason to prevent dialing. In addition, with the advent of end-to-end signaling, phones with polarity guards were needed to prevent blocked dialing after call completion that might involve inadvertent polarity reversals.
We're glad you got it straightened out. I would not trust any tester made by RS, though. The best tester is the phone itself. An experienced repairman can pretty much tell wazzup just by listening to the sub's phone.
