I had a friend at work that had his retirement income figured incorrectly and they wanted it back after a year. It was discovered when someone else retired and they figure his wrong as well. That guy knew his business and corrected them. They went back to check and found this other guy's was figured incorrectly as well.

He was working for a company that was bought out. The employees were given a lump sum for that time served for retirement. The new company was not supposed to honor those years served. When they figured his retirement, they gave him credit for those years. They ending up in a lawsuit because he would not have retired. They ended settling out of court. He was able to keep the extra money for that year but his retirement was reduced from that point forward.