The answer is, there is no one answer unless the manufacturer has defined the rating method per an IEC or maybe EIA test method.
We know for sure that your "100W" tweeter cannot handle 100W continuous power, or not even 60W continuous power. Thus, logical to conclude its 100W rating is intended to imply the tweeter is suitable for use in a 100W speaker system. And, based on the distributions shown in the chart, reasonably is expected to handle just a small fraction (10-15%) of the total power, on a music-type duty cycle, not continuous.
All one has to do is look at the tiny wire and small area of the tweeter voice coil to understand the continuous power handling capability must be small indeed.