It's easy to imagine we don't have the first year of writing, maybe the first human lifetime of writing, but it stretches imagination to invoke a situation where somehow a civilisation is writing clay tablets for hundreds of years, decides they are not to be made into permanent records and somehow they're so lucky that there's never a house fire, a goof at the bakery, somebody's kid spills hot stuff on the tablet, nothing like that and so over that period every single tablet is destroyed/ erased as expected and leaves no trace.