this is exactly what has happened
was on 4.2.0-9 then updated with a 4.5.0 Firmware Title
thus updating it to 4.5.0-9
the final digit is purely Online Features version number
i have a 3DS on 4.5.0-0 and 4.5.0-4
When I bought my 3ds xl 2 months ago it was 4.2.0-9 out of the box. In anticipation of getting a gateway (or R4i) I borrowed Donkey Kong Country returns and updated and it gave me 4.5.0-9. When I noticed that this firmware didn't seem to exist on the list I started panicking that I did something wrong, especially since I could have left it at 4.2. Anyway, R4i was ordered and used and now I also have Gateway and there seems to be no issues. I even tried to get it up to 4.5.0-10, by re borrowing the DK and even trying Luigis mansion but both games did not show the update screen.