Think of each published quarter as a photograph taken on the edition date. The engine asks: "How old is this model on that date?"
Roll forward one quarter and the same manufacturing year is older. Depreciation schedules and age bands advance, so retail and trade typically decrease. Cost new in the database might be flat while values still move - that is normal.
Use the price history tool on a model (where available) to see the curve across quarters. Comparing printouts from different editions without noting the quarter will confuse customers - always label the edition date.
Sudden jumps without a quarter change may indicate a data correction or multiplier update; compare release notes or ask an administrator.
Why age affects value each quarter
Each quarter ages every model by the same calendar step; values usually fall over time even when cost new is unchanged.