Yes shift is important. If your receiver has positive shift, the crystal has to be higher by the IF (intermediate frequencey) of the actual transmitted frequency, if Negative shift, it has to be lower than the transmitted signal. For single conversion, the IF frequency is 455 Killo cycles, for dual conversion, it is usually 11.7 megacycles. Plus, some recievers use 3rd order harmonics while some use 5th order so again, diferent brands of receivers may require different cuts of crystals to work properly. It is not simply an act of matching frequencies.