Static Thrust
I'm also curious to know more, because FAR 25 is pretty clear on requiring the OEM to account for thrust variation with, for example speed.
25.101(c) states:
...performance must correspond to the propulsive thrust available under ... the particular flight conditions..."
So unthinking use of static thrust would appear to be a contravention of FAR25 - unless it is shown elsewhere in the cert that this is conservative, of course.