For (5),its dimpling.When a sheet of material is too thin for countersinking,knife edging will occur and the hole may also open up if its way too thin.A countersunk hole should not affect the drilled hole size.The hole in this case would be dimpled using a special tool but its not a very common practice nowadays on larger a/c.Last dimpling I did was on an ATP eons ago!When you find the possibility of this happening on larger a/c skin repairs (when you have to open holes up to the next size),most manufacturers call for protruding head fasteners to be fitted as long as the repair isn't in a critical airflow area.Hope this helps!