New Measure to Compare Date between Different Table

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How it works ....
This measure will return all valid staff (just in case there is  ore than one)

Valid staff = 
VAR customer = SELECTEDVALUE('SALES VOLUME'[CUSTOMER])
VAR saledate = SELECTEDVALUE('SALES VOLUME'[SALE DATE] )
VAR mysubset = 
FILTER('SALES INCENTIVE', 
'SALES INCENTIVE'[CUSTOMER] = customer  
 && 'SALES INCENTIVE'[FROM DATE] <= saledate 
&& 'SALES INCENTIVE'[TO DATE] >= saledate 
)
RETURN
CALCULATE(
CONCATENATEX('SALES INCENTIVE','SALES INCENTIVE'[STAFF],", "),
 mysubset )