Wondering why some parts don't fit

[Isitjustme?]

New here and have a question about part fitment. My daughter and I are working on a '72 K10 SWB that she bought a couple of months ago (pics in the 'welcome' thread). We've done a lot to it and fixed a fair number of problems on it but have come up with some odd fitment issues.
For example, we did a brake job on it and found the e-brake lines at the drums were torn up badly. Ordered a set specific to her truck, but they don't fit. Almost 3" short. Went to several local parts stores and all showed the same item. Finally figured out that we need the listed cables from a Blazer, not a K10. The VIN confirms her truck as stated and I looked around the frame to see if it had been altered. Near as I can tell, it has not.
Another example, the back up lights weren't working. Traced that the the neutral safety switch on the steering column so ordered one. It didn't fit. Not even close. Our column has a smaller diameter than the new switch and the activation tab is completely different. It looked like the switch from a '73 might fit, but I managed to repair our old one, so didn't pursue that.
Last example is the lower radiator hose. The listed hose for a '72 was shaped differently than the one I had in my hand, but we took it on faith. It didn't fit. Again, not even close. Went back to the parts store and found the hose for a '73 matched our design, but the radiator side was 1/2" narrower than the radiator outlet. Oh, and the radiator mounting pieces were also shaped differently than ours, but we altered them enough to fit them in place.
So anyone else run into this? Or have any thoughts as to why we're running into this? Maybe a late model 72 and someone just thought it might be fun to put newer parts on?