Why the inconsistency between 2001 and 2012, the two odisseys of Clarke?

I started to read 2012 and i don't understand why some of the facts of 2001 are different from what the characters say in 2012. For example:

• The most obvious one, Discovery one travels to Saturn in 2001, whereas in the second odissey, they say that it went to Jupiter.


• The monolith, AMH-2, is on Saturn in 2001, while on Jupiter in the second odissey.


• HAL is called CARL (in french) in the first book

Theories:

1. Clarke adapted the second book so it follows the movie plot. Implying Clarke is unfaithful to his readers


2. There is another theory: Clarke thought that such journey to Saturn would be possible in 2001, but considering the technology at the time, he knew that it would be difficult, whereas Jupiter is closer to reach from the Earth, therefore more realistic to undertake in 2001. Which isn't very likely because travelling to Saturn just requires more fuel than Jupiter.