This employee was treated badly by his or her employer, who warned him or her to “forget what they know” or face legal action. And they carried out their ex-instructions boss to the letter. When the tower of cards their boss had forced them to construct ultimately came crashing down 10 years later, the same boss was left with only one option: ask OP how to fix the whole thing. It’s simply a shame the instructions had all vanished and the OP had dutifully neglected the crucial facts. It’s a pity, it’s very sad.
What’s interesting is that this previous employer was in such a desperate situation that they had to return on their knees to an employee who they could have kept if they hadn’t been so desperate. The story is instructing, let us make you read it in OP’s own words. Don’t forget to tell us your feedback about it in the end.