No matter how much fertilizer a substrate may have when you first install it you need to supply more fertilizer over time.
Think of the substrate as your plates and bowls. The fertilizer is like the food. Keep on using the plates and bowls, adding food for each meal.
The substrate should last for years, but you need to keep adding fertilizer.
Your use of the plates and bowls really helped me understand and visualise the importance of substrate what what it does. Thank you both for taking the time answer my question.