"Usually" that data is found in characterization data for the device. The fact
its not speced means it either is not reliable for spec sheet, eg. a part of
test procedure that could predict what performance would be or its simply
a parameter with bounds so great not worth repeating. Or given testing it
hot, there are simple methods to do that, test time too great a cost burden.
Contact production EE responsible for device, or rel department, to see if
they can lend any comment.
Regards, Dana.