Most valid questions, and let me add a clue. What is a "stone age context" to the artwork uncovered, when I can construct a picture of Tony Blair on the side, right now, if no one stops me? Yours is the most pertinent of questions, but the simple answer to me is graffitti or high art can be added at any time after its initial construction. By the way, the orientation of the easterly King can possibly be dated by his posture. Kings were oriented usually due East or due West during their era of life/death. Since due East/West changes over the millenia, a sharp eyed individual can measure the offset from today's due East/West, I believe, to guesstimate a time frame. Also, the hair style of the "Queen", showing the Ram's horn, the time of Aries/Ram. And the crown of the King, almost a Fez, could identify the culture, possibly. Your question is eminently valid.