Don

1. My understanding is that later written Scripture cannot contradict earlier written Scripture and this is true throughout the Bible.  This is related to the idea of progressive revelation.

Of course, they need to be understood in context, text out of context might appear to contradict other text.  When you find an apparent contradiction, it is a big clue that you need to dig for more context to better understand one or both texts.

2. It only takes one statement for a law to be a law.  Some things are written many times in Scripture, some only once; they are all true.