Comprehensive and Detailed 150 to 300 words Explanation From Exact Extract of Agile Project Management (paraphrased):

AgilePM’s MoSCoW prioritization is always applied within a defined timeframe (e.g., a release or timebox). A requirement can be a Must Have for a specific delivery window while being a Should/Could when viewed across the whole product roadmap. Timeboxing, dependency considerations, and the need to deliver a coherent, usable increment by a certain date mean that priority is inherently time-contextual. While budget and resources influence overall planning, AgilePM fixes time and cost to provide predictability and flexes scope to protect quality; thus, the most legitimate driver for a requirement’s priority to change is the timeframe to which MoSCoW is applied. As delivery horizons shift (e.g., near-term release vs. later release), the same requirement’s priority may be re-appraised to ensure the Business Case and Product/Release Goals are met. Therefore, Different timeframe is the correct reason that explains variations in backlog priority.