It seems I have to repeat myself, but let me try again. I think you're missing the whole point of IPSAS - "real debt" isn't the absolute number owed at some point in the future. If I owe you $1B, due a zillion years from now, I'm not really in debt $1B. The only reasonable way to measure debt is based on it's market value.

That's because someone would be willing to trade that debt with me for owing about $1 a year from now. They are equivalent.