Exactly -- that means that any analysis based on the current (as of 1926) 'reserves' or 'production capacity' for rubber/fertilizer/coal/wood would have been invalidated as soon as we switched to using oil instead. Imagine if instead of harvesting helium directly we find an economic way to split nitrogen (somehow, who knows). At that point, what you'd have to have forecasted would be the 'reserves' of nitrogen, which are functionally infinite.