Technological change has been a constant since the beginning of the industrial revolution. But what was a difficult technical challenge and what wasn't is sometimes difficult to remember in retrospect.
For example, this Shorpy photograph shows a street in 1935:
The really step into the scene, go to the full size image on Shorpy.
Every car on the street, even that Packard limo in the lower right corner, has a rubberized canvas insert in the roof, pointed out by Dave, the brains behind Shorpy. It turns out that it wasn't until the 1935 model year that GM was able to design and build a giant (and expensive) stamping press that would create one-piece all-steel automobile roofs. Eventually those became standard. I had no idea.
That's why I'm so nervous about writing historical fiction. There are just so many details that are easy to get wrong--though this is a great detail to include. But my favorite, Shorpy, remains an invaluable resource, both for the photos and the informative comments. And the mordant Dave.