No matter if you've been baptised in another religion it don't matter because once you joing the JWs' you are an unbaptised person, because you have not been baptised into their religion.
An interesting thing is that prior to 1985 2 questions that they asked were something like 1. Have you repented of your sins and turned around, recognizing yourself before Jehovah God as a condemned (ouch!!! terrible to be condemend) sinner who needs salvation, and have you acknowledged to him that this salvation proceeds from him, the father, through his son Jesus Christ ? 2. On the basis of this faith in God and in his provision for salvation, have you dedicated yourself unreservedly to God to do his will henceforth as he reveals it to you through Jesus Christ and through the Bible under the enlightening power of the holy spirt?
Then they changed it to...1 on the basis of the sarifice of Jesus Christ, have you repented of your sins and dedicated yourself to Jehovah to do his will? Do you Understand that your dedication and baptism identify you as one of Jehovahss Witnesses in assocaition with God's spirit directed organization????? Holy spirit has gone outta the window here....