550 rev limit question

The factory manual states max rpm is 7500. Various magazines state the limit as 7700rpm. In fact the max speed as listed in the owners manual, 199mph (320kmh) can only be reached in 6th at 7700rpm.
The workshop manual states that max rpm is 7500rpm, but further that the Bosch ECU intervenes at 7240rpm and starts cutting the ignition. My experiments on the dyno with my own car have shown that the rev limiter does indeed cut in at approx 7250rpm, with a soft limiter that cuts entirely at 7500rpm. Reading my tacho, however, shows the soft limiter coming in at 7500rpm with lights out at 7700rpm.
My question is, is this behaviour normal, or is the workshop manual wrong?(which would not be out of the question) Should the limiter be cutting in at 7700rpm instead?

 

Dan
Thanks for the feedback. I wasn't sure if tyre slip on the dyno was causing the difference.