The idea of four Man-Kzin wars comes from the Known Space series, and they occur at a much later period of fictional history in that universe, in the 25th and 26th centuries. "The Soft Weapon" takes place in the 27th century.
I like The Slaver Weapon
a lot, but I recognize that it basically shoehorned
Known Space into the Trekverse, so I don't demand that it seamlessly meld with it.