Earlier quoted context omitted.
Congress isn't the same Congress that passed the bills.
That's a good point. I don't really have a sense for whether the legal system makes any differentiation between different sessions of Congress, or whether it's just viewed as one continuously-operating entity. Like would Congress be able to retroactively-clarify their intent if the law was very recent and the same Congress was still in session?
Congress as an institution is one continuously operating entity. But the important question legally is not what Congress is, but what the actual text of the statute passed by Congress and signed by the President is. That is the law. In other words, the Constitution does not say "whatever Congress says is the law". It lays out a specific process by which laws get passed, and says what the limitations of that process are (no ex post facto laws, which means Congress can't pass a law that says some previous law meant something different, and have that retroactively apply).
> would Congress be able to retroactively-clarify their intent if the law was very recent and the same Congress was still in session?
No, but they could pass a new statute repealing the old one, or replacing it with new language, which would limit the time the old statute was in effect.