A concussion management review panel in December highlighted shortcomings in Northampton's handling of the incident.
World Rugby expressed "disappointment" that Northampton let Wales wing North return to the fray after he fell heavily following a tackle by Adam Thompstone in a December game against Leicester.
But after conducting a review of the matter, it followed the lead of a concussion review panel convened by the Rugby Football Union and Premiership Rugby by electing not to punish the club.
"Despite the failing by the club to correctly apply World Rugby's head-injury management protocols, World Rugby has recognised that the RFU and PRL (Premiership Rugby Limited) acted swiftly and appropriately to implement measures with Northampton Saints and other clubs to reduce the probability of future non-compliance," World Rugby said in a statement.
North, 24, appeared to have been knocked unconscious after being challenged in the air by Leicester wing Thompstone during Saints' 19-11 Premiership defeat on December 3.
After a head injury assessment he returned to the fray, but World Rugby has now confirmed he should have been taken off.
North was subsequently stood down by Northampton for three weeks in the latest head injury issue to have affected the Welshman's career.
He previously had to observe a five-month break in November 2014 after a succession of concussions.
A concussion management review panel in December highlighted shortcomings in Northampton's handling of the incident in the game against Leicester, but did not impose any sanctions.
World Rugby said the RFU and Premiership Rugby have since reminded all English rugby stakeholders "of their obligations to ensure that immediate and permanent removal is observed in all such cases".