Upside-down Number Plate

While going through "Human Computer" Shakuntala Devi's book on puzzles, I came across one which I liked very much. In fact, all the puzzles are good but I liked this particular one because it was the only one I could solve, and that too after spending days trying to figure it out.

Let me state the puzzle in my own way. I saw a vehicle, which bore a characteristic number. The number was characteristic because it could be read upside down also. When I say it could be read upside down I don't mean an observer could figure out the number. What I mean is that if the number plate was fixed upside down, an observer wouldn't realize it; he would think the number plate was fixed in the proper way and the number of the vehicle that he was seeing was the correct number. At the expense of giving the game away, I think I must explain. Now, consider the digit "9"; if the digit 9 is written upside down, it will still be seen as a legitimate number, but will appear as 6. If, on the other hand, you see "3" upside down, you will be able to figure out it is "3", but you will at once realize that you are looking at an upside down number. Got it?

The registration number consisted of five digits (all of them different). If the number plate was fixed upside down, the number that the observer saw was different from the actual one and it was greater than the actual number by 78633. What is the actual number?

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