Okay! Based on what I'm used to seeing, you're missing probably 15 holes on that fender. It seems they get added along the way for extra "things" that get bolted on.
Here's what I have.
First the horn bracket. There are 4 holes (I don't know why since all the brackets I've seen only have 2 holes) centered over the hat channel - this location must have been chosen to provide extra support vs. on just the sheet metal fender.
Notice they aren't perfectly centered on the hat channel shoulder. I'll bet there may be differences from one jeep to the next - just as long as they are on that hat channel shoulder for mounting support. Also: Notice the wire clip just below and slightly behind the horn bracket holes.
From above:
From below:
The horn bracket holes are measured from the front edge of the fender.
One more measurement from the top edge down to the hole:
To mark the back 2 holes, measure back 1 7/8" from the front holes. I think you could also use your bracket to confirm this (again probably not critical since one hole on the bracket is actually a slot for adjustment).
The image you posted is of Lawrence Wade's '55 jeep. Here's another that I sent to another member concerning the 3-post junction for wires and it just shows the first horn bolt at the very edge of the image (with the empty hole below the bolt).
(I added this as I don't see marks for the 3-post junction).
There are more holes needed for the wiring. Added: This is an image I got much later of Wade's fender showing harness along the fender:
Those extra holes I'm guessing may have been used to align the sheet metal during assembly. Additionally, if you look at the holes above that show the horn mount holes from the top - you'll notice the sheet metal holes and the hat channel holes aren't exactly lined up. This also makes me think the parts are drilled separately then aligned during assembly.
