This used to be the case, but these days it is no longer true for many colleges. Although it remanins true for some. Harvard AOs have said recommended = required. Princeton has said recommended = optional; it can help if you submit, but it won’t hurt if you don’t. I don’t follow Cornell closely enough (and their change is recent) to know their philosophy.
That said, I remain firmly in the camp of send zero or two. Virtually nobody takes one Subject Test, and sending one can signal that the applicant is hiding a score, which he is. And in this case, I’d opt for 0. With time running out, I would retake SAT or ACT before taking Subject Tests again.