There have been several notable SCOTUS cases in the past that we can point to from the present that have played defining and/or developmental roles in course of U.S. history. At the time the decisions of many of these cases were handed down the Court realized their potential impact. For example, Marbury v. Madison established the power of judicial review. Chief Justice Marshall* recognized the potential for carving out the Court's power in that instant and he was deft in his writing of the opinion. This has stood since as law, but at the time it could be construed an impermissive expansion of control by an overreaching newly established Federal government.

Another example to look to where the Court recognized the potential for long term impact is Dred Scott v. Sandford. In that case, the Court held that African Americans, irrespective of their status, could not be U.S. citizens, and thus had no standing to sue. This was a defining moment of Antebellum race relations at the time, solidifying through law the status of slave states. Today, this is often cited as one of the worst SCOTUS decisions of all time and it was one of the precipitating factors of the Civil War. Obviously society does not today agree with the decision (which was overruled by the 14th Amendment), but at the time it was intended to end the slavery question.

You mentioned Plessy v. Ferguson, affirming "separate but equal" segregation. Certainly this is no longer good law nor a reflection of today's society. It was overturned in Brown v. Board; however, by an an entirely different Court over half a century later.

These example above mentioned are easy to point to, well known decisions. The Court that made them sometimes reflected the society of the time they lived in, sometime was reactionary, and sometime was very omnipotent in their forethought. Sometimes decisions of little to no impact at the time have established the basis for grand swings in Court opinion.

There are almost innumerable cases SCOTUS has reviewed that are still good law and almost as many that are no longer law or no longer controlling - most you've never heard of, if for no reason other than they don't impact individual's daily lives. The reasons behind the changes vary almost almost as widely as the cases themselves, but many are as simple as the Court has changed its mind. This could be because the composition of the Justices have changed or more generally because the times have changed.

In sum, the Court does "screw up" sometimes - you often see this in the dissenting opinions that have subsequently become law. Or maybe it's not a screw up at all, but a change in society or the Court itself. However, until another case comes along challenging previous decisions and the Court agrees and overturns their past rulings, the past holdings stand and control all cases like them. Citizens and their lawyers challenge standing decisions all the time, it's the most effective way to change and define existing law.

Thus, you should look to Supreme Court opinion - nay, you have to look at their opinion. Their decisions are law until another decision overturns the previous one (or Congress acts on the subject). Citizens and their lawyers challenge standing decisions all the time, it's the most effective way to change and define existing law.

*Fun side note: Thomas Jefferson was a cousin of John Marshall, and they disliked each other immensely. Jefferson considered him traitorous to Virginia because of his strong Federalist views, going so far as to say Marshall was “poisoning the public mind and gaining a passport to posterity." Historian Henry Adams commented on Marshall, "This great man nourished one weakness. He detested Thomas Jefferson…no argument affected his conviction that Jefferson was not an honest man.”

Sorry, but could you clarify your question a bit? I'm not sure I understand what you're asking.