Okay, but dgallow at https://news.ycombinator.com/item?id=48589728 asked "Have we actually forgotten how to land to the moon?", not "can we build a Saturn V rocket which is fundamentally the same as the ones from nearly 60 years ago?"

Reading about the design for the F-1B engine gave me some understanding of the issue.

The F-1B was meant as a modernized version of the Apollo Saturn F-1 main engine.

The original design used extensive hand-welding, and the specific details of how to handle tricky situations likely not included in the manufacturing processes details because it was simply expected from an expert welder of the time.

That sort of expertise is far less common now. But rather than try to find those welders, the designers of the new engine used newer methods like additive manufacturing to replace welding entirely.

The old F-1 engine used a lot of complicated mechanical control methods. The F-1B used computer controls.

The new design had fewer components, was lighter, and was designed for a 15% performance boost over the original design.

So, sure, perhaps we can't exactly build a new Saturn V rocket following the 1969 blueprints, due to missing production floor changes. But we would never try because we are not limited to 1960s building methods if we wanted to use the Saturn V design as the basis for going back to the moon.