EXTRADATA is already end of life and not part of the next version 1.52 anymore. It was a trial to approximate open and close prices of a bar period through (high+low)/2 of the first and the last bar to enhance the speed of the backtest but with remarkable drawbacks of the strategies' performances. See also on What's New:
Zorro 1.52 new features (in development)
...
The EXTRADATA flag of version 1.50 was replaced by the LEAN flag that has the opposite meaning. Historical data is now stored in noncompressed format by default.
Or in short words: use EXTRADATA always to receive accurate results.
