It is theoretically possible to construct an algorithm with a complexity growth curve that is shifted on the x axis. In other words, you might get part of the left side of a parabola as well as the right for an O(n^2) algorithm if the algorithm happens to have a particular value of n that it performs best at were you to graph the algorithm’s runtime.

This is a fairly unimportant point, but it’s one that traditional algorithmic theory doesn’t really touch upon.