How relevant are the 300,000 employees? Do they all had access to this information?
If you read the link in my previous comment, you'll see this isn't the first time they got fined for bad record keeping practices. In that instance, $125m.
It's kinda either/or. It's either possible that someone can get full admin privileges and deletes it off-the-record or they've got enough safeguards in place that the accidental deletion isn't possible either.
I don't think your argument works unless the article is wrong.
the thing we're discussing is deleting A LOT of records which INCLUDE the ones being subpoenaed, which is obviously easily possible, intentionally or otherwise
so, no stretch of the imagination required