Many thanks for your comments. There are two ways in which we are working to integrate data and statistics from other organizations. Many data series that are in the current catalog, particularly the World Development Indicators, are in fact sourced from organizations such as the UNSD or FAO, and we make special efforts to document these sources. For individual indicators such as Forest Area the citation is just under the description at the top of the page. For datasets, the "Source/Citation" metadata field provides this information where appropriate.
The second point of integration is to link our country pages to country-level open data portals where possible. This is still a work in progress, something we hope to roll out later this year.