Can I ask if JW's believe that God's original creation was perfect solely on the the Genesis account or do they use other Scriptures too?
There are some scriptures that can be seen to imply that, yes:
Deu. 32:4 "His work is perfect, all His ways are just"
Ps. 19:7 - "The Law of the Lord is perfect"
Matt. 5:48 - "you are to be perfect, as your heavenly Father is perfect"
Some of them seem to point more to his personality and laws, perhaps, but I see no reason why it wouldn't also apply to his works (as Deu. 32:4 does indeed state).
-There's also the thought that Jesus was the "second Adam", and that the reason Jesus could atone for our sins, was that He was perfect just as Adam had been, and that Jesus was the only one who could offer a worthy ransom because all other humans were imperfect. Granted; to JWs, Jesus is not God, but even so it would be weird if Jesus was perfect and not God.