Until recently the difficulty with this solution has been that the collection of URLs deteriorates over time as sites disappear, pages are reorganized, and underlying content changes: For example, in April 2002, we attempted to download the documents in the STRAND English-French, English-Chinese, and English-Basque collections, and we were able to access successfully only around 67%, 43%, and 40% of the URL pairs, respectively.
the Internet Archive's Wayback Machine provides a way to distribute persistent URLs.