Is there a word for the bias of not knowing what came before?

Solution 1:

recency illusion

The name of that bias is recency illusion. Recency illusion is a cognitive bias arising from a misbelief that something one's noticed just recently is also recent itself, thus believing it to be a new discovery when it is actually already long-known— or "old news," as you put it.

Recency illusion is a cognitive bias commonly reinforced by the Baader–Meinhof phenomenon, which occurs when one suddenly starts noticing something one's noticed for the first time so frequently that as frequency of noticing it increases, so too increases a belief in it being unlikely to have failed to notice it ever before. That increasing belief tends to lead to a strengthening belief that that something can't have existed before because one would have noticed it before and so that something must be new, a basis for the formation of a recency illusion.