Coordinative compounding is well recognized as one of the major tools for coining new words in Chinese, but its role as evidence of grammatical change has long been ignored. In the Tang-Song era (AD 618-1279), a redundant form of coordinative compound 了也 liao-ye comes into being in the process of the new marker 了liao replacing the old marker 也 ye. Similarly, a redundant form 已了 yi-liao occurs in the process of了 liao replacing 已 yi. These two liaos correspond to Mandarin Chinese sentence-final 了 le and verb-suffix 了 le respectively, the origin of which is a puzzle to many Chinese historical grammarians. The present study discusses the problematic issues of the history of different 了 liao/les and suggests 了也 liao-ye and 已了 yi-liao disclose where they are from. The disclosure is taken as support for a hypothesis that redundant coordinative markers are formal evidence of grammatical change in Chinese.