What would cause contributions and contacts to go missing?
1/ unlikely to be upgrade related

2/ assuming you have access to 'log' tables you can write an sql query to identify records where the first/last names have changed from the previous log record

3/ if you mean how to find and prevent in future, use the logs to try and identify who/when and figure out what the person was trying to do and train them otherwise (assuming user error at backend) OR if problem occured by front-end process then perhaps check your Matching rules