Look at what you're saying.

I'm assuming that by ``fallen'' you mean ``committed a sin''. You say that if he hadn't fallen, then he would have been able to follow the law perfectly, where the law is defined by what sins are, so that following the law perfectly means never to commit a sin.

So your statement

If Adam had not fallen he would have been able to follow the law perfectly as well.

is easily translated to:

If Adam had not [committed a sin] he would have been able to [commit no sins]

I don't see that that has any meaning.

However, it is possible that my assumptions about what you mean in certain places are wrong.