This issue of Cash Box, dated July 24, 1965 would have been published a week earlier, on July 17, and would have gone to press a day or so before that.  The whole magazine can be seen here; the image below is taken from page 6.  The typesetter seems to have got mentally snagged on Dylan's title, as the following album, Percy Faith's Broadway Bouquet, is mistitled Broadway Revisited . . .

From a very similar report in Billboard (also dated July 24), it seems that the announcement was made at Columbia's sales convention at Miami Beach, 14-17 July (for which Dylan had recorded a message at Levy's studio in London the previous month).  Dylan was perhaps pressured into giving Columbia a title for his forthcoming album which could be announced at the convention, and just came up with "Highway 61 Revisited" off the top of his head.   If this was how it came about then the title song probably came later.  For some reason, Billboard's news item does not mention any release from Dylan, though the source appears to be the same as for the Cash Box article.