Thanks for remark. You are right cached pages are sent to visitor browser without Last-Modified info in the page header. The change shall be included in next update of JotCache.
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(Article in russian language - "JotCache review. Joomla 3 caching") Very detail description of JotCache features, installation hints, evaluation of site loading without & with JotCache
In this tutorial is shown how to install the JotCache Extension in Joomla 3. JotCache provides more in-depth control of caching in Joomla. There are described 3 steps to installing the JotCache Joomla Extension.
Joomla extensions that can significantly speedup the website: JotCache and Cache Control are both extensions that can help you controlling what is cached and what should be excluded. NoNumber Cache Cleaner is really good for cleaning up cache automatically.