Chris Doss : Heidegger is describing the structure of meaning. He's not interested in its source. It's not a theory of development. ;) Questions such as what you are talking about are probably not addressable using phenomenology, with its first-person standpoint.
Heidegger in the second part of B & T does discuss history in relation to Dilthey and someone else whose name I can't remember (he's forgotten today). But that is in the context of describing how the past is interpreted in the present as part of the anticipation of the future.
^^^^^^
CB: So he is focussed on the here and now, today, literally, a real presentism. Sounds like his theory is a structuralism.