Well your dates are off! Your theory is nonsense.
The phrase "Minnesota Nice" gained popularity in the mid-1980s, with its first documented appearance in a newspaper in 1986. It was further popularized by cultural figures like Garrison Keillor through works such as A Prairie Home Companion and Howard Mohr's 1987 book How to Talk Minnesotan. However, its origins are tied to the state's Scandinavian immigrant heritage and agrarian history, reflecting values of politeness, emotional restraint, and aversion to confrontation
Meaning of "Minnesota Nice":
The term describes a cultural stereotype of Minnesotans as polite, reserved, and mild-mannered. It encompasses behaviors such as friendliness, self-deprecation, and avoidance of direct conflict. While often seen as genuine kindness—helping neighbors or refraining from honking—it is also criticized for masking passive-aggression and emotional aloofness. Some view it as a facade rather than true niceness
. Scandinavian influences emphasize humility and community over individualism, shaping this cultural norm.
Minnesota Nice did not even exist for Cooper to use in 1971. It hadnt been invented and popularised yet to be in the pubic consciousness, for Cooper or anyone else to use! So your theory is nonsense.
"Dan Cooper" was inspired by a comic book hero popular in Europe during the mid-20th century, which may explain its use as an alias but not as a common given name. Agent Carr has suggested that DB Cooper got his name from the comic book.
You are beating a dead horse which has no factual reality ! Take your loss for once and drop this nonsense.