That's true. But the wiki gives alternatives for both cases. If you learn both algs, you can perform the alg from whichever direction you like. If you get the first case, you can perform the first alg. If you get the second case, well perform the second one. For example, if you just learn the first one and get the second one, it would be terrible to do a y2 THEN perform the first alg. Or a U2 D2' which is worse.