Structures built in Minecraft not loading from old save, despite clear evidence for them in save files

You could try running the save file through MC edit and see if its there. Because you stated that it showed that it was there in the save file, you could copy your creation to another world(made using your new computer). That allows it to reload the chunks in a new world made by you new computer.

Get MC edit here: http://khroki.github.io/MCEdit-Unified/

Best luck on getting your creation back.

I suspect what is going on is that there are 2 different ways of rendering your world and probably that bit of chunk that is not default failed to load hereby not showing it in your world.