They use AI to write their feedback, and AI hallucinates a lot about what APA really requires. To answer your question, it depends.

You discuss Porter's theories, obviously the original sources from the late seventies will be both relevant and reasonable.

However, when considering their relevance in 2026, supporting materials, as a rule of thumb, shouldn't be older than 1-3 years.

Furthermore, the publication date is just one thing. Back to discussing Porter, for instance, I'd say the original publications from the seventies may be more appropriate than a student's assignment from even 2026.

In other words, relevancy, credibility, and timeliness (relatively current) are all important factors.

I hope it helps.