Could the maesters have used an oral tradition or runic script before the arrival of the Andals brought a new writing system and culture shift that supplanted and obscured the older customs of the First Men maesters?

The runic script seems the most likely, but the discrepancy between the way WOIAF talks about the First Men’s language and the timeline makes me think either that something has been deliberately obscured or something really bad happened that caused a massive break in historiographical continuity. .