Suppose a player has reached a higher stage in a tournament but failed to reach the same stage in the next year.
Can you explain how the ranking will be affected for each stage worse they are placed the next year?
Points awarded for ATP rankings are dropped after 52 weeks (slightly less than a year). So generally it doesn't matter what your previous performance in tournament X is; only your 'new' performance matters, and the awarded points are documented in various places, e.g. Wikipedia.
Of course, with the pandemic tournaments may be shifted on the calendar and affecting the ranking differently (it's a 24 month ranking right now IIRC), but let's hope that's a temporary situation...