Lookup table based on other table

MYDATASTORY , Ideally you should have a date table with FY to be part of your date table. Not clear what is the issue.

To get the best of the time intelligence function. Make sure you have a date calendar and it has been marked as the date in model view. Also, join it with the date column of your fact/s. Refer :
https://radacad.com/creating-calendar-table-in-power-bi-using-dax-functions
https://www.archerpoint.com/blog/Posts/creating-date-table-power-bi
1.Creating Financial Calendar - From Any Month
https://community.powerbi.com/t5/Community-Blog/Creating-Financial-Calendar-Decoding-Date-and-Calendar-1-5-Power/ba-p/1187441

examples

YTD Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESYTD('Date'[Date],"12/31"))
Last YTD Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESYTD(dateadd('Date'[Date],-1,Year),"12/31"))
This year Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESYTD(ENDOFYEAR('Date'[Date]),"12/31"))
Last year Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESYTD(ENDOFYEAR(dateadd('Date'[Date],-1,Year)),"12/31"))
Last to last YTD Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESYTD(dateadd('Date'[Date],-2,Year),"12/31"))
Year behind Sales = CALCULATE(SUM(Sales[Sales Amount]),dateadd('Date'[Date],-1,Year))

Hi, MYDATASTORY , as info is limited, what I can do is to make a best guess and a possible solution is to resort to TREATAS func to establish a virtual relationship dedicated to such a lookup. The measure is like this,

FY Lookup = 
CALCULATE (
    MAX ( 'Data Table'[FY] ),
    TREATAS ( VALUES ( Sales[Date] ), 'Data Table'[Date] )
)

Date column comes from Sales table.