There is not a single version of the test where 26 is the maximum possible score. Based on certain versions, a 30/29/28 is the lowest science split I've seen produce a 30 TS, and not even that guarantees that 28 was the highest possible score in that subsection.
The difference between a 21 and a 27 is at least a handful of questions, which is not as few as it sounds considering there are only 30-40 questions per section. I'm not sure where the misconception comes from that the people scoring at the very high end were just lucky enough to get another question or two right because it's not that basic.