Learn English – What does “but” mean

In this case, aye almost certainly does mean always. For one thing it makes perfect sense contextually. Moreover, the connection with Scottish actually makes a lot of sense. We learn from Morag, in another answer, that aye is still used in Scotland. Even if it weren't, archaic English or Scottish would not be out of place in this song.

The Watson Family lived in the Appalachian Mountains, a region settled by Scottish and Irish immigrants. Difficulty of travel kept them functionally isolated, and the pre-radio music of that region is known for strong ties to old ballads of Scotland, England and Ireland. Here's a great radio piece about this history: http://hereandnow.wbur.org/2014/10/01/wayfaring-strangers-book

The corpus of Appalachian folk music also includes a lot of references to political roles that never really existed in the U.S. - Lords, ladies, knights, kings, etc. Examples abound here: http://www.contemplator.com/america/index.html

It means that not only the headline annual economic growth numbers of China are important to the rest of the world - China's other monthly economic data is important to the rest of the world too.

China's annual economic growth numbers and other monthly economic data are all important to the rest of the world.

China's annual economic growth numbers are important to the rest of the world and so are China's other monthly economic data.