According to my 1980 Cymbal Setups of Famous Drummers guide, the Swish Knocker at that time was Heavy, while the Swish was Medium-Thin.If you click on the link I gave earlier to the big pdf of model introductions and deletions, you will see that the 2010 year I mentioned is the last year for the "older" style knocker. Then in 2011 (laser serial starting AA ) it was redesigned based on the original Mel Lewis Village Vanguard cymbal. So there may not be a gap in production from the 1979 Swish Knocker to the 2011 Mel Lewis version. Just a replacement of one with the other in 2011. So says Zildjian anyway. What I'm not sure about is what might have been happening in the 1950s and 1960s. The big pdf really only kicks in at 1970. The Swish itself goes back to at least 1938 (Zildjian filed a patent on it), and I've got examples from then as well as the mid 1950s. But as I said I'm still not sure how the Swish Knocker is different from the Swish.
Here is a second one from my site, along with the 1939 catalog showing it: