I believe that was due to the fact that previously one could file for back credits once   a SSN was obtained.
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This explains it very well.
ITINs: The Rules Have Changed 
[...] In the past, taxpayers could claim an EITC, a child tax credit, or the American opportunity tax credit on an amended or late-filed return with an SSN or ITIN obtained after the return's original due date. However, this will not be the case going forward...
https://www.thetaxadviser.com/issues/2016/jul/itins-rules-have-changed.html
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Can I amend previous years tax returns ITIN's with the new SSN's
2017 EITC Income Limits, Maximum Credit Amounts and Tax Law Updates
https://www.irs.gov/credits-deductions/individuals/earned-income-tax-credit/eitc-income-limits-maximum-credit-amounts-next-year