[stevendhansen]

I have a guess: the limit in these designs isn't typically the motor, but instead the power semiconductors in the inverter (the motor has a much longer thermal time constant than the power devices). Therefore the limit is the junction temperature of the power devices. Most high performance drives have some kind of junction temperature estimation algorithm (it is difficult or impossible to put a sensor right at the junction without changing the electrical properties of the semiconductor). When the estimated temperature gets too high, they will start pulling back the current to protect the power devices from overheating. The more accurate the model, the closer they can push the devices to the limit without failure.

I'd bet they have been slowly improving their junction temp. estimation model and are now able to push the power semiconductors a little bit closer to their temperature limit, allowing them to produce more current (or the same current for a longer duration) before pulling back.