Thanks for your comments, peacefulpete,
It has already been discussed on this forum that copies of the Septuagint prior to the second century CE do not translate the tetragrammaton with Kyrios ("Lord"). Likewise, while there is evidence that some regarded the divine name as too sacred to pronounce prior to the second century, the fact that a Greek version of the name (Iao) was in use at the time of Christ indicates it was still in regular use.
Regarding the Karaites, the same Wikipedia article you quoted from says :
According to Mordecai ben Nissan, the ancestors of the Karaites was a group called Benei Ṣedeq during the Second Temple period. Historians have argued over whether Karaism has a direct connection to the Sadducees, dating back to the end of the Second Temple period (70 CE), or whether Karaism represents a novel emergence of similar views.
Whether Karaism as a movement arose in the seventh century, or existed in one form or another since the destruction of the second temple, it remains true that they were still using the divine name in the tenth century CE.
While rabbinic Judaism with its emphasis on oral tradition was the prime successor to what had existed before destruction of the second temple, there would have been many from other groups who retained their identity and were not bound by rabbinic tradition. These would include the predecessors of the Karaites.