They cannot be both at once. They are depicting a single age, a single "moment in culture." That age is certainly sundered from the Mycenaean prime by the century or two in which changing ideas led to the superseding of burial by burning, or it is sundered from the Mycenaean prime by a foreign conquest, a revolution, and the years in which the foreign conquerors acquired the language of their subjects.
In either alternative, and one or other must be actual, there was time enough for many changes in the culture of the Mycenaean prime to be evolved. These changes, we say, are represented by the descriptions of culture in the Iliad. That hypothesis explains, simply and readily, all the facts. The other hypothesis, that the _Iliad_ was begun near the Mycenaean prime and was continued throughout four or five centuries, cannot, first, explain how the _Iliad_ was _composed_, and, next, it wanders among apparent contradictories and through a maze of inconsistencies.
We are far from contending that it is always possible to understand Homer's descriptions of defensive armour. But as we have never seen the actual objects, perhaps the poet's phrases were clear enough to his audience and are only difficult to us. I do not, for example, profess to be sure of what happened when Pandarus shot at Menelaus. The arrow lighted "where the golden buckles of the _zoster_ were clasped, and the doubled breastplate met them. So the bitter arrow alighted upon the firm _zoster_; through the wrought _zoster_ it sped, and through the curiously wrought breastplate it pressed on, and through the _mitre_ he wore to shield his flesh, a barrier against darts; and this best shielded him, yet it passed on even through this," and grazed the hero's flesh (_Iliad_, IV. I 32 seq.). Menelaus next says that "the glistering _zoster_ in front stayed the dart, and the _zoma_ beneath, and the _mitrê_ that the coppersmiths fashioned" (IV. 185-187). Then the surgeon, Machaon, "loosed the glistering _zoster_ and the _zoma_, and the _mitrê_ beneath that the coppersmiths fashioned" (IV. 215, 216).
Reading as a mere student of poetry I take this to mean that the corslet was of two pieces, fastening in the middle of the back and the middle of the front of a man (though Mr. Monro thinks that the plates met and the _zoster_ was buckled at the side); that the _zoster_, a mailed belt, buckled just above the place where the plates of the corslet met; that the arrow went through the meeting-place of the belt buckles, through the place where the plates of the corslet met, and then through the _mitrê_, a piece of bronze armour worn under the corslet, though the nature of this _mitrê_ and of the _zoma_ I do not know. Was the _mitrê_ a separate article or a continuation of the breastplate, lower down, struck by a dropping arrow?