Yeah, clearly Nevada have the models mixed up. Being the OP, I confirm I now realise I actually have a classic J, not a contemporary, so thanks for clearing that up. I have tried to clarify with Chris May, but I've found before Overwater's email response is not in the same class as their luthery so nothing's come back.
Like Mornats I have always until now had great experiences with Overwater strings, and what's more they're very cheap. I have no idea why these weren't any good. But I do find strings aren't just the twangy bits that give truss rods something to do. The same string can sound very different on different basses. I used to run Overwater nickels on my Hohner 6 and they absolutely sang, while D'Addario nickels wrestled the richest sounds out of my Peavey Grind 5. But when I tried swopping them over neither set sounded anywhere near as good.
What's I've found in this case, for me personally, my Overwater Classic J loves D'Add flats, but YMMV.