Previous_Value_as per Day_range

Prev_Value =
VAR CurrentYear = SELECTEDVALUE('YourTable'[Year])
VAR CurrentMonth = SELECTEDVALUE('YourTable'[Month_Number])
VAR CurrentCustom = SELECTEDVALUE('YourTable'[Custom])

RETURN
CALCULATE(
[Avg_Value],
TOPN(
1,
FILTER(
ALLSELECTED('YourTable'),
('YourTable'[Year] = CurrentYear && 'YourTable'[Month_Number] = CurrentMonth && 'YourTable'[Custom] < CurrentCustom) ||
('YourTable'[Year] = CurrentYear && 'YourTable'[Month_Number] < CurrentMonth) ||
('YourTable'[Year] < CurrentYear)
),
'YourTable'[Year], DESC,
'YourTable'[Month_Number], DESC,
'YourTable'[Custom], DESC
)
)