Not always a set number(sometimes one or two extra, leading to annoying score discrepancies), but there are particular planes/ships in particular locations that always get neutralized.
This usually happens when you take out the last plane and it's one of them that become neutralized. What will happen is you will still see it start flying away, and if you hit it with your guns, you will get a destroyed message, but you don't get the points for it.
If you fly flicker of hope, you have to watch which one of theF-16's that you take out. Usually go for the one on the right, he will be neutralized, then the one on the left.