how about the following explanation on the usage of 'since' and

来源: 于 2015-07-30 19:48:51 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

Chinese stock market continued to fall on Tuesday since three weeks before ... =
Chinese stock market continued to fall on Tuesday since the starting of the fall three weeks before the fall on Tuesday ...

Googled and found the following interesting on 'before', 'ago' and 'earlier':
http://www.italki.com/question/111799