Ji, 22, made four league appearances in 2013-14 before leaving for Augsburg in January, the striker agreeing terms for a summer move to Borussia Dortmund a day later.
The Premier League strugglers – who are second from bottom in the table – claimed an administrative error led to the blunder.
And Sunderland officials have been left red-faced after being handed a fine for the incident, which they confirmed they were made aware of in December, paying the subsequent penalty earlier this year.
The Wearsiders will be relieved, however, to have escaped further punishment in the form of a points deduction, which would have severely dented their survival hopes."The issue of Ji Dong-Won was explained in detail at today's Premier League shareholders' meeting and no issues were raised by any club," said a statement on Sunderland's official website.
"Sunderland AFC confirmed that they had complied with all procedures and the Premier League stated that the player was duly registered on the extranet system and in all other Premier League mechanisms.
"The club has never accepted any wrongdoing, but did acknowledge that a technical fault occurred and as such were fined by the Premier League accordingly in December.
"The matter is now closed."