Name the thing that must be true
For a plan, it might be arriving on time. For a report, it might be accounting for every input row. For a comparison, it might be including the real cost of a required add-on.
Find a check outside the answer
Use the calendar, the original rows, or the official source. Asking the same tool if it is right can be useful conversation, but it is not independent evidence.
Try a changed input
Move the appointment, add another week of data, or change a priority. A repeatable result should respond for a reason you can explain.