1. Part Number Prefix (656V vs. 656L): This distinction typically indicates an iteration in the internal crystal element, IC die, or manufacturing process batch/revision. It does not alter any defined key performance parameters. The manufacturer may have implemented cost optimization, a supplier change, or a process improvement while ensuring full compliance with the standard specifications (frequency, stability, voltage, current, interface) of the previous version. Therefore, they maintain a direct drop-in replacement relationship. 2. Potential Unspecified Characteristics: While the datasheet parameters are identical, the letter change may imply minor optimizations not explicitly listed in the standard parameter tables. These could include slight improvements in phase noise, marginally enhanced long-term aging characteristics, or differences in ESD robustness. In the vast majority of applications, these differences are imperceptible and do not hinder direct substitution. However, for extremely stringent RF or high-reliability designs, final validation via bench testing or consultation with the manufacturer is recommended.