"You do realise that the US Treasury currently values most its...

"You do realise that the US Treasury currently values most its gold reserve bullion at $42.22 oz? So if the students at ISIL were to mark-to-market collective gold in global government reserves it would show an increase in value, regardless of the prior date."

Incorrect. If they had to mark-to-market then their statements would have shown an increase in the value of their stock bought prior to 2011 and a decrease for that same stock since then. This is what the weakest of the ISIL students would immediately recognise. It is an ongoing period process with the stock being evaluated at fixed intervals.