I don't agree that there is anything random about it. The Sting is loaded with optical transitions such as wipes, dissolves, & fades, and the shots with DNR are generally the leading and trailing shots surrounding those transitions. Universal must have opted for DNR in those shots to soften...
One of life's delightful little ironies is that David S. Ward was unhappy when Universal chose to settle a plagiarism suit from The Big Con author David W. Maurer out of court, as while Ward had used the book as a source, is is non-fiction and it was just one of many such sources that he used...