Jon Searles' photos with the keyword: flat

I'm not aware of the precise history of #44312, but I do note that it's of wood construction, with screw couplers (it looks like) leaf springs and two carbody-mounted axles, but with automatic air brakes. Therefore, it could be quite old, although some mid-19th-century design features survived on CSD into the 1940's, so looks can be deceiving. I do not that at the moment 44312 is being used to store steam locomotive parts.