I do not recall the lock logs option having such a feature. A change was made in mIRC v6.21 (some time after multi-server support was added) that used a logging filename format that included an id number eg. name.N.log to distinguish log filenames in multiple connections to the same network. However, this was reverted in mIRC v6.3 by popular request, as many users did not like it. I cannot remember the reasons why - perhaps it added yet another level of complexity to log file naming, parsing, processing, reading, etc. that users did not want. There are no plans to add it back again I'm afraid, not even as an option.