The copy of the '76 lectures I possess has a disclaimer stating that the formulations in the book were superior, and the course was made available for those who might find it instructive to compare the differences.
Perhaps the credit that Peikoff deserves is not for his ability to have preserved the “letter of the law”, but to have captured the “spirit” of Objectivism in a well organized presentation.
Her redacted public notice came out prior to the '76 lectures. As the composer of Objectivism, hers are the official scores. Furthermore, her verbal endorsement here was affixed to his verbal delivery.
If anything, more benefit could probably be derived grasping the steps and criteria that establishes what can be taken as objectively true, and being able to communicate it in such a way that others find enrolling.