I’m old enough to remember James Kilpatrick’s columns on usage and the like. His advice on apostrophes with words ending in “s” was to treat it as you would say it. In the example in the video, most of us would say Norris’s car. Since we would say it, Kilpatrick would have agreed with the video that we should write it with an apostrophe-s even though the word ends in “s.” The video also refers to Greek names such as Aristophanes. Most of us would not say “Aristophaneses.” Hence Kilpatrick would have agreed with the video that we should simply add an apostrophe after the preexisting “s.”
My caution is that I have never seen anyone else set out Kilpatrick’s rule.