Boy, this is a tough one.
Could striations occur during forging? Absolutely. Could these parallel lines have been created by the drawing of the bar, pre forging? Absolutely. They aren't exclusive to each other.

But why show up years after initial finishing?
Differential corrosion.

That would suggest that a mild acid would reveal their continuity.
Discontinuous? Probably scratches.

Out there doing it best I can.