Basically 0 CAD models you see with color coding and a mesh are actually accurate. In order to mesh the geometry for finite element analysis, the geometry virtually always needs to be defeatured. So the cross sectional CAD model here is a nice curiosity but basically useless for any reverse engineering purposes which is the key reason this stuff is kept secret.
In Germany we say "The DIN knows non color". DIN is our standardization organization and informally also how their documents are called. I did finite element model preparation for a living many year ago and it did not only involve heavy defeaturing but interestingly also remeshing with quads. Renderers love triangles, FE solvers love boring quads.
yeah there are several adaptive meshing techniques that use a mixture nowadays, imagine a bar with a hole bored through it, you might use quad meshes for the majority of the bar and then switch to tetrahedral meshes close to the bore hole to better model the curved geometry of the hole, and increase the node density in high stress concentration regions for a more accurate simulation.