That's the strangest thing George ??
You have 2 PCI and a PCIe slot that you cannot use.
The removable section that you have hold of is an "optional extra" - so the original design was for the 3 slots that, from your photos, cannot be used.
Does the plate with the square grill holes come off ?
Mind you - it doesn't look as if it should.
I will see if I can find a manual.