Computer managers have it drummed into them that they must keep back ups of every activity. Hat attitude is ingrained. As time has gone on, and storage costs have all but disappeared, that attitude is re-inforced. Whatever a computer record now says, in any commercial organisation, there are likely to be several earlier backup copies. If it is felt or suspected that a record may have been altered, go for the back-ups.
Computers are lazy.
What is deleted is not always deleted. Indeed, Windows now makes a virtue of this. A file may be thrown in the rubbish bin, but then, as with a piece of paper, it can usually be retrieved. We understand that a rubbish bin itself may be emptied, and the rubbish bin on the screen also metaphorically emptied. What is not quite so obvious is that even after that, the file itself is not removed from the hard disk.