Spudqueen, I have no great interest in the Jack the Ripper story and just provided the opening answer above, as it seemed pretty straightforward and easily linked-to. Thus, you are quite likely to be right as regards earlier theories about Sickert...I wouldn't know.
However, I think it unlikely that anything published over 20 years ago had much to say about DNA evidence which - as best I recall the book - was a significant element of Cornwell's theory. Maybe, therefore, just a little more than a mere "raking-up" of old stuff! But...what do I know?