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The singer is Rubén Cané, and this version is from 1953-02-02. The same version of the song appears on Angel D'Agostino 1941/53, Coleccion 78 RPM by Euro Records, 2004. In addition to 1940, Vargas recorded 'No aflojes' in 1954 with Trio Alejandro Scarpino, but the version in question on Lantower has a full Orquesta tipica on it. I have just listened to other songs with Rubén Cané on Euro Records and on Archivo RCA, and I'd say that's a match. Report by Martin Rybczynski.