This probe is less commonly used nowadays. I saw it mounted on large machinery like forced draft fans in power plants where the speed is relatively low. It's more common on balancing machines (feild or shop) specially from IRD. Some portable (route) vibration programs use this type of probe also.
I can't give a definite answer to your question but my guess based on my understanding of this sensor is that the dynamic range (125 mil pp) would be the reliable reading range from the generated electric signal while the probe travel (375 mil pp) would be the physical movement of the internal component before it hits the design limits. The term dynamic range here is used in a different context to what some practionors use.
I'll see if I can have one of these sensors and measure the travel to verify my guess. As you may know there is more than one design of these. Some have an extended rod (perhaps 1/8" dia, 1" longe, opposite side to the cable) that measures the vibration. The sensor can measure vibration as the rod moves.
I hope this helps a little.
Regards- Ali M. Al-Shurafa