How the 45 RPM Single Changed Music
rollingstone.com
rollingstone.com
I'm confused, they did exist and there were shellac/78rpms which were red prior to that. The color was used to denote the genre.
Seems like it means impossible to overestimate, easy to underestimate, or just impossible to estimate.
The author surely meant 'impossible to overestimate.'
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I don't know if this is a common mix up, like, for example:
"I could care less." (which means you have not reached a minimum of caring)
vs
"I couldn't care less." (which means you have reached minimum of caring)
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Or the more pernicious (in my opinion) and pervasive:
"Not all X are Y" (some X might be Y, but at least some are not)
vs
"All X are not Y" (There are no X that are also Y)