From what I have seen they all have the 2 on top and 2 on the bottom and are never used. I would say that they were tooling holes.
If I came across a car with no top holes it would make me think that there was something dodgy going on. eg- a new chassis number welded in.

I can only say that my car had holes everywhere only half of which seem to be used...the rest had rubber plugs...

After having another look at the firewall photo, it may well be that an oval binnacle has been fitted at some point, as there are two holes either side of the central aperture which seem to fit the outer fixing screws of that binnacle.