Logging Like a Pro by Neal Hu via @ITNEXT_io

Theories and best practices on effective application logging.

I think logging is critical and a log is just as much a piece of data worthy of reporting against as something containing customer or order information. This is the place where you get clues about what is wrong with the system, where you find out who deleted what, and conversely who added what. 

Another option is to also add a flag to every record in a file that signifies if it was added, updated or deleted. Then you don't lose data. Think about that combined with a log to capture the update details.