There are plenty of “area’s” in Nuendo (and other applications) where you can check the length & framerate of the video. What does the Original video say in the Pool? according BITC? In QT? In G-spot or another application.
What doesyour audio shows in these same area’s?
Import audio from video file. What is the information of that audio file?
If there is a difference between your exports and the stuff you received from the editor, then something is wrong with your system/setup. This really sounds like you are clocked to the wrong samplerate. Which is possible since you are not using a House/Sync clock. So gather all the information you can, and compare the stuff you have been receiving with the stuff that you have send back.
Fredo