If they had time, it would have been much more effective to corrupt or -- better -- heavily modify the data in a plausible way. For example: Changing dates and times, or swapping names with other names, inserting or deleting parts of sentences. Moving them around. Use phrase generators with plausible phrases to add records. They could even take advantage of Unicode to flip characters between character sets in an identifiable manner so that they can be identified when posted in the wild.

It wouldn't take much corruption to make them question the value of the files that weren't touched, and because of that they might end up nuking their own data (maybe even their backups) just to ensure that they aren't using tainted data.