It seems that the scoring for fields and cities in Carcassonne varies -- has this changed over the years, or is this a difference between the US and international versions? Are there generally-accepted correct scoring rules for fields and cities?
The third edition scoring is now what is shipped by both Rio Grande Games(US distributor) and Hans im Glück(Original, German publishers)
Rio Grande Games made the changes for the english version of the game (1st and 2nd edition scoring).
Here are a summary of the scoring rule changes by edition
Rio Grande Games only recently (2009) starting shipping the 3rd edition rules, while Hans im Glück issued them in 2004. The reason given is that RGG prefers not to issue rule changes when reprinting a game. This meant that they had to rewrite the rules of most expansions issued to ensure they were compatible.
I do not believe that Jay Tummelson (Head of Rio Grande Games) has stated why the switch was made in 2009. I think there are two possible explanations.
There are three versions of the Carcassonne rules; citing Wikipedia:
I would imagine that tournaments will typically use the newest official version of the rules, but for recreational play there is no such thing as "correct" rules. Use whichever version your co-players and you agree on.