Since Isaiah 43:10 was written to the nation of Israel, then the pre-Christian Jews were Jehovah's Witnesses.
Good point Sparky1 ,
And did the pre Christian Jews ever identify themselves as Jehovahs Witnesses by name ?
No of course not it was never meant for them to convey Gods chosen people be called by that name /designation.
Why not ? because of what is written in scripture at Acts 11:26b "and it was first in Antioch that the disciples were BY DIVINE PROVIDENCE CALLED CHRISTIANS"
THEY WERE NOT CALLED Jehovahs Witnesses.