How many years can a liquid fuel rocket be safely stored (unfueled) between manufacturing and launch? Are they sensitive to slow processes like corrosion, material degradation from dehydration, other chemical processes, seasonal temperature variation, fatigue of load carrying structures, gathering of dust that can clog or cause a fire, or biological activity by microbes, insects, rodents, or a combination of all above? Would it take much to store a launcher safely? On the other hand, they are robust machines built with high quality materials.
For example, an ambitious human mission to Mars would require several launches, preferably within a brief period. Some expect, maybe pessimistically, that only one SLS will be manufactured per year. Could they be saved up for a decade to then be launched as frequently as the space port capacity allows?