Create a calculated column for prior year

RingoMoon , Try using below method create a new calculated column, replace column and table name 

Prior Year =
VAR CurrentYear = [EventYearRevenue]
VAR PriorYearRevenue =
CALCULATE(
MAX([EventYearRevenue]),
FILTER(
ALL('TableName'),
[EventYearRevenue] <> BLANK() && [EventYearRevenue] < CurrentYear
)
)
RETURN
IF(ISBLANK(PriorYearRevenue), BLANK(), PriorYearRevenue)

This should do the trick

Prior Year = 
VAR _CurrentYear = SolutionAlex[Year]
VAR _PriorYear = _CurrentYear - 1
VAR _FindYear = 
    CALCULATE(
        MAX(SolutionAlex[Year]),
        SolutionAlex[Year] < _CurrentYear,
        NOT(ISBLANK(SolutionAlex[Revenue]))
    )
VAR _Value =  CALCULATE(SUM(SolutionAlex[Revenue]), ALL(SolutionAlex), SolutionAlex[Year] = _FindYear)
VAR _Result = 
IF(
    ISBLANK(_Value),
    BLANK(),
    _Value
)
RETURN
_FindYear

If you want the Prior Year, then return _FindYear as in my DAX, if you want the associated revenues, return _Result.

If it answers your query, please mark my reply as the solution. Thanks!

Don't forget to change the table name 'SolutionAlex' with your tableName

Hi RingoMoon ,

You can do it in Power Query or using dax.

Power Query:

• Sort the table by event and by year
• Add the following column

try
  if #"Added Index"{[Index]-1}[Event] = [Event]
then
 #"Added Index"{[Index]-1}[Revenue] else null

otherwise 
null

DAX

Add the following column:

VAR temp_table = SUMMARIZECOLUMNS(
		'Table'[Event],
		'Table'[Year],
		'Table'[Revenue]
	)
	RETURN

		SELECTCOLUMNS(
			OFFSET(
				-1,

				temp_table,
				ORDERBY('Table'[Year]),
				,
				PARTITIONBY('Table'[Event])
			),
			'Table'[Revenue]
		)