Every project will will save its history. This will show the the project administrator what has been changed in that project, when, and what was the original value. Just by clicking on the the history button on the top-right corner in every project, you you'll see that information. 
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In the result you will see:
Date of change
The user who made the change
The field that was changed
Original value
New value
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⚠️ You will only be able to view the history of fields that do not have visibility restrictions.