Some secondary websites to verify the legitimacy of the URL:

• https://library.ifla.org/id/eprint/1089/ Lessons learned from twelve years’ operation of the Web Archiving Project (WARP) (PDF page 2)
• https://netpreserve.org/about-us/members/national-diet-library-japan/

Extracting the archived date from archived pages on WARP is tricky because the data is embedded into the page, and its format depends on the language you choose on their home page https://warp.da.ndl.go.jp/

Example archive page:
https://warp.da.ndl.go.jp/info:ndljp/pid/9597364/www.dus.emb-japan.go.jp/profile/japanisch/j_wirtschaft/j_DUS.htm
When you specify "Japanese (日本語)" on WARP's home page as
https://warp.da.ndl.go.jp/?_lang=ja
then the date portion in the archived page will show:
"ご覧いただいているのは国立国会図書館が保存した<span class="warp_textArea_collectDate">2016年1月6日</span>時点のページです。"
In this mode, the date format is yyyy年m月d日.
https://icu4c-demos.unicode.org/icu-bin/locexp?d_=en&_=ja_JP

When you specify "English" on WARP's home page as
https://warp.da.ndl.go.jp/?_lang=en
then the archived page becomes:
"You are viewing an archived web page captured on <span class="warp_textArea_collectDate">6 Jan 2016</span> by the National Diet Library, Japan."

By default, they seem to ignore the browser's setting for "preferred language for displaying pages" and always show pages with Japanese format (tested with Firefox, clearing all cookies and setting the Webpage Language Settings to "English [en]" on top). But I am not certain here.