Octane at high altitude

If you haven't watched the video below, I would recommend watching it because it cites research on this subject and has some surprising results. Spoiler, on cars manufactured after 1987, high altitude has little affect on the octane requirement of an engine.

With that said, I want to draw some attention to one part of the video which this screenshot is from. There are 2 things I want to highlight.

• The difference between the red and blue lines on the graph. The test was done on old carbureted engines. The octane requirement for engines at sea level that used 100 dropped to 85 at 10,000ft while the red line which was 85 at sea level dropped to 50 at 10,000 ft.
• For newer cars (1987+), the text under the graph which shows a much smaller difference.

My question. In the 1942 data, there was a much greater difference (35 points) for the 85 compared to the 15 points on the 100 octane. With the newer test, the comparison is only made for the 100 and I would expect it to be better than 0.2/1000ft for 87 pump gas. I don't have access to the complete article. If anyone has a .edu email address with a school library account, please enlighten me. https://www.jstor.org/stable/44469205