Further to JT's post.
The RAF Tristar fleet was a little perturbed a few years ago when a civilian contractor was able to lift more than them from a rather restrictive airfield in a dusty place due to the fact that Boscombe Down had used the older UK standards for RAF ops while the contractor had the same type but with an FAA AFM which gave them a 12 kt lower vmcg. Same jet different rules different max take-off
