We know they existed, but not much else.
In fact, none other than the Kojiki itself states that its stories are collected from contemporary works (which have all been lost). This is because the Kojiki was a compilation. It was the product of a royal effort to collect "historical" texts in circulation at the time, to edit into a relatively coherent narrative. And propaganda.
From the Kojiki's own preface,
We heard that chronicles collected by other families are inaccurate and contains many fabrications. If this is not corrected now, within a few years the true message would dissipate. Therefore we compile this chronicle, examine the old tales to remove false narratives and pin down the truth for the future.
Thus, it is certain there were earlier works, but unfortunately none has survived. The Kojiki (and later the Nihon Shoki were somewhat political in nature for justifying the legitimacy of the ruling house. Thus natural attrition due to time and lack of government patronage aside, contrarian records likely faced a hostile environment when it comes to preservation.