The BoM for the CY4608M Development Kit calls for a customised crystal "CRYSTAL 12.000 MHZ 20PF 49US (Drive Level: 600uW, Tolerance: +/- 50ppm)". The only difference I can see between this and a standard ECS-120-20-4 is that the drive level is 600 uW compared with the standard 500 uW. Has anyone used a standard 500 uW crystal in their designs and seen aging (frequency change) problems?
We had a similar requirement and higher wattage crytal was not available. We added a series resistor along the crystal and made sure crystal drive strength was within specification. The setup worked in our lab for long time across temperatures and it worked. you can consider doing that.