A written record may encode a stage of a language corresponding to an earlier time, either as a result of oral tradition , or because the earliest source is a copy of an older manuscript that was lost. An oral tradition of epic poetry may typically bridge a few centuries, and in rare cases, over a millennium. An extreme case is the Vedic Sanskrit of the Rigveda : the earliest parts of this text may date to c. 1500 BC,  while the oldest known manuscript dates to the 11th century AD, a gap of over 2,500 years. Similarly the oldest Avestan texts, the Gathas , are believed to have been composed before 1000 BC, but the oldest Avestan manuscripts date from the 13th century AD. 
It seems more responsible to carve out that area of spirituality closest ‘in spirit’ to the other intelligences and then, in the sympathetic manner applied to naturalist intelligence, ascertain how this candidate intelligence fares. In doing so, I think it best to put aside the term spiritual , with its manifest and problematic connotations, and to speak instead of an intelligence that explores the nature of existence in its multifarious guises. Thus, an explicit concern with spiritual or religious matters would be one variety – often the most important variety – of an existential intelligence.