It required nails to hold the layers together in an age where glue was less...Super.
Nails in early times were fairly brittle. While you could get fairly maleable iron, most nails were not. and you could not afford to buy special nails just for the door. When you bend over or clinch a nail, a maleable iron nail could be straightened and reused. Very frugal you know. Usually a nail was driven through all layers and clinched over inside to make a very durable slab of wood that would not separate.
It was not uncommon to burn a house to the ground when leaving an area, just to recover the nails from the ashes. If your nails were not maleable iron, they could not be straightened out again, so they were said to be dead nails.
So, here is the expression.... dead as a door nail. Many nailing patterns were very complicated. In this case, I kept it very simple.
Who knows, in a couple of days I may look at this and decide to add a hundred more nails to the pattern.
And I re- cut the frame around the window to straighten it.