create unique list from multiple column

Hello everyone
i have 4 column have data in number of row 5990 , i want to create new column with only unique value from 4 column
i used this formula

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but it give me only 40 value then 41 give #REF! error
i dont know why


also i want to know if applicable after create this unique list , every row from unique list can referee to which column is mention from 4 column
i attached example to explain what im looking