Make a search on the Web for the term Triple I demo. YouTube, archive.org, or some other site should have the video. You want the video Triple I (1976 1979). It is a compilation of two different demo reels. You can tell the change by the soundtrack. But it's also important to see how they used art direction to get the most out of what they were able to do.
Watch it now and enjoy it.
That is quite an improvement over the work in Sketchpad, but still very stiff. Work on color, lighting, and textures was all being done for the first time. What is amazing is that this was a professional demo reel. Now, it might not even get you a job as an intern. Back then it was amazing.