Table Repeat value based on other column

PatCreator  Thanks for your query.

Here is my solution:

1. Create a calculate column for Date in the table using the below DAX:

Date = 
VAR MonthNum = SWITCH( 
TRUE(),
'DataTable'[Month] = "January",1,
'DataTable'[Month] = "February",2,
'DataTable'[Month] = "March",3,
'DataTable'[Month] = "April",4,
'DataTable'[Month] = "May",5,
'DataTable'[Month] = "June",6,
'DataTable'[Month] = "July",7,
'DataTable'[Month] = "August",8,
'DataTable'[Month] = "September",9,
'DataTable'[Month] = "October",10,
'DataTable'[Month] = "November",11,
'DataTable'[Month] = "December",12
)
VAR Result = DATE( 'DataTable'[Year], MonthNum , 1)

RETURN
Result

Table Snapshot:

2. Create a measure for Baseline:
Baseline =
VAR MinDate =
CALCULATE (
MIN ( 'DataTable'[Date] ),
ALL ( 'DataTable' ),
'DataTable'[Year] = SELECTEDVALUE ( 'DataTable'[Year] )
)
VAR Result =
CALCULATE (
MIN ( 'DataTable'[Pop Coverage] ),
ALL ( 'DataTable' ),
'DataTable'[Year] = SELECTEDVALUE ( 'DataTable'[Year] ),
'DataTable'[Date] = MinDate
)
RETURN
Result

Output Snapshot:

Hope this helps.