No idea whats going on with the different trim values with the same/different Rx's, but you could check something with the resistors. Did you measure their actual values before fitting them? Like all components they have a tolerance and although I doubt it, you may have one near the bottom end of the range and one near the top. Measuring them with a multimeter would rule this out, but be sure to un-solder one end of each resistor before measuring it. Long shot, but worth a check.