Legal Question in Constitutional Law in Virginia

Article 1, section 8 of the U.S. Constitution is pretty broad. I presume you're asking about the part that authorizes Congress "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries".

That clause applies to Congress, not to writings, discoveries or other works. It allows Congress to enact intellectual property laws. But does not say Congress must do so, and it does not dictate what those laws should say.

Of course, Congress did decide to create intellectual property laws. Those laws, and not the provision you cite, are what apply to particular works.

If Congress decides to increase the duration of copyrights, it can choose to apply that change to new and existing works or only to new ones. It can also apply it to some existing works and not others -- for example, only to those less than ten years old. The Supreme Court ruled a year ago that Congress may even restore expired copyrights, taking the works out of the public domain. The same is generally true of other types of intellectual property rights.