cores
You are right. GDFv5 script consist of analyse stage and frame-recovering stage. Separate frames from-the-future and frames from-the-past are detected and must be fixed correctly. You can control it by parameter myDebug=true.
You can see frames marked from '-fix50' to 'fix125'. It is mean -50% from source (back to the past) and +125% from source (go to the future).
Usual dropped frames must be marked 'fix50'. It is mean from the futire in the middle from current frame and next frame to avoid jump after dropped frame.