It should be easy to distinguish a primary source from a secondary source, a first day exercise in all my classes.
A primary source is one written or created during the era you’re studying (such as a letter, diary, newspaper article, artwork). A secondary source uses primary sources to make a more general statement after the fact (a journal article, textbook, newscast, for example).
The next step adds nuance. What about a newspaper article written in 1869 about the Peloponnesian War? This would be a secondary source for the Peloponnesian War, but a primary source for 1869. It can tell us something about 1869 that people were interested in the Peloponnesian War.
“Historical” movies cause a similar issue. A film made in 1970 that is set in the 19th century West is a secondary source for the 19th century West, but a primary source for 1970 (or just an exercise in enjoying Clint Eastwood).
So far so good, but what about sources that aren’t factually correct in their “primary-ness”?

I’m talking about documents like the Protocols of the Elders of Zion, purported to be a report of a group of Jews trying to take over the world by undermining Christian morals and dominating the economy. It’s considered a “literary forgery”, but it had an impact, particularly in encouraging anti-semitism. It’s not a primary source for the supposed Elders, but it is a primary source for studying those in the 20th century who printed it, distributed it, used it, believed it.
And now I belatedly discover a more benign, perhaps, version of this trend. Chief Seattle is frequently used in primary source document sets to portray the 19th century Native American view of white incursion and cultural genocide. But the actual sources, it turns out, are cobbled together from unverifiable documents.
I don’t use Seattle for my classes, so I was unaware. Where did I learn it? From a tweet about the Historical Association materials for teaching. The page on Interpretations had some resources for teachers about citizenship, and even though this would be British citizenship I thought it might be helpful. Certainly as I go back to the classroom to teach US History, I should focus more than ever on the responsibilities we all have as American citizens.
The Teaching History article by Andrew Wenn gave an excerpt from Seattle, which I’d seen before:

This was then followed by:

“My own feelings”? That sounds like today, where things that didn’t happen are considered true because they fit with pre-conceived notions. Naturally I had to look this up, so I plugged in “I have seen a thousand rotting buffaloes on the prairies left by the white man” and Google took me to a book that had a very long version of this as if it were utterly legitimate. It’s also in a recent book on “wilderness wisdom” as a speech. It’s in class materials for a faculty member at the Community College of Baltimore County. Those are the first things listed in Google Search.
Of course, further down on the results there are sites noting it’s bogus.
Wikipedia covers it as a story of the screenplay Ted Perry was writing, and reveals what the producer did with it in terms of publicity.
So this bogus document is clearly a primary source (I’d argue a very good one) for the environmental movement of the 1970s. There are all sorts of topics here: the role of movies in environmentalism, the use of Native American ideas to support the movement. It’s also possible that bits and pieces of it came from Chief Seattle, somehow — it just can’t be verified. Some would say it portrays the “feeling” of the Native Americans, or the Suquamish or Duwamish people particularly. Which is fine so long as we understand it isn’t a verifiable primary source for them at this time.
Given the use of truth and lies in contemporary political and social discourse, I’d say the balanced approach might be too nuanced for community college students. Showing such things as lies and forgeries seems right, but perhaps it’s just a new form of what happened when scholars joyously tore down the images of people like Thomas Jefferson. Historians were still buzzing from Fawn Brodie’s 1974 analysis of Jefferson and his relationship with Sally Hemings when I started in the field. That book may have been the start of the trend toward knocking people off statues, a trend no doubt assisted by the fall of Richard Nixon that same year. Now even Monticello is just a slave plantation.
Unfortunately, such efforts, while enhancing professional history, did not contribute to depth in popular culture. Just the opposite. People went from worshiping former public figures to denigrating them without restraint. Where previously such critical examination had been a scholarly exercise (I think of Charles Beard in the 1910s revealing the Founders to be men of property designing government in order to keep it), it became popular fun.
As this fun continues, with the wholesale denigration of former famous people as if they had no “good side” at all (I think again of J. Marion Sims or, for that matter, Robert E. Lee), it may not be the time to get into the nuances of forged sources. Those which inaccurately combine multiple sources, or which are attributed to people not responsible for them, should probably be tackled as they emerge, rather than presented as part of an introductory exercise.
But I’m still surprised about Seattle. And embarrassed that I’m surprised.