Formula IFERROR Calculation Error

I am attempting to convert a text field of 8 digits into formatted date. The majority of the entries are in yyyymmdd order, but more than a few are in yyyyddmm order, so the original date_format formula is erroring on the rogue entries. IFERROR should return the result of the first formula unless it errors, in which case it should return the result of the second formula. This is my construction:

IFERROR(

 DATE_FORMAT(CONCAT(

  SUBSTRING(`Valid To`,1,4),'-',

  SUBSTRING(`Valid To`,5,2),'-',

  SUBSTRING(`Valid To`,7,2),'%Y-%m-%d')),

 DATE_FORMAT(CONCAT(

  SUBSTRING(`Valid To`,1,4),'-',

  SUBSTRING(`Valid To`,7,2),'-',

  SUBSTRING(`Valid To`,5,2),'%Y-%m-%d')))

This is the error message: Calculation Error : Function DATE_FORMAT expected 2 arguments but got 1. The first DATE_FORMAT formula successfully converts yyyymmdd values into legit dates. How do I get the IFERROR part to move to the second DATE_FORMAT formula if it doesn't? Thanks in advance for any help.