there are many mnemonic devices strewn throughout the text of the Illiad and the Odyssey, for example, 'rose-fingered dawn' shows up many, many times as a 'stopping point' for remembering.

There are many, many different manuscripts of the Homer's works which all had minor or major differences, depending on who wrote them down - there's one project that tries to pull them all together: http://www.homermultitext.org/about.html

Only relatively recently has there been 'one' Iliad, before that it was whatever the orator remembered, and memory isn't perfect