You should not label anything "reference only." That's an like an engraved invitation to an auditor, asking him to start digging. The standard says that devices must be calibrated "if necessary to ensure valid results." If you feel like a given device doesn't need full-blown calibration, you should label it "Calibration not Required," and be prepared to provide the rationale. Also, "calibration" is nothing more than comparing a device to a standard, and doesn't imply adjustment. There are different levels of calibration. What's commonly referred to as "verification" of a device is a form of calibration.