Could demand-pull inflation occur before an economy was producing at capacity and how?

Yes, demand-pull inflation can occur before an economy reaches full capacity if there is a sudden increase in aggregate demand that outpaces supply. This can happen due to factors such as increased consumer spending, government stimulus, or investment booms. Even if there is slack in the economy, the heightened demand can push prices upward as businesses respond to the increased demand by raising prices, anticipating future shortages. Thus, demand-pull inflation can emerge even when there are unused resources available.