As an illustration of how worn out #20 was, here is the diaphragm plate from #20's smokebox. If you look at the first photo above, it is the plate that goes behind the steam pipes shown. The writing is on patches that are not original, and were added at a later date
Here is the back side of the same sheet. The staggered hole pattern is the result of cinders blasting out of the tubes that have worn completely through the original diaphragm plate, resulting in the need to patch the sheet to keep from setting the countryside on fire.
Here is a low angle view of the same sheet. Even where it isn't worn through divots are worn in the sheet in front of every tube hole. This is indicative of the condition of the whole locomotive. Boy, was she shot!