Ive read, that The Impressions & Jerry Butler - For Your Precious Love, is believed to be one of the first records termed as 'Soul', I think thats Dave Godin who wrote that... see its released in 58, so a little after some of the dates mentioned above, maybe the term was used in conversation allot earlier, but as a marketable release, perhaps the Impressions was just that?
there are far more knowledgeable folk on here of course, so I'm happy to be educated...
Mal