When my level 70 mentors down to do a zone invasion in an old zone, I often get obsolete currencies, Void Stones and Abyssal Crusader's Marks, rather than the level 70 currencies. Sometimes I get a mix of obsolete and current currencies.

For example, I just ran a Golden Embers event in Freemarch and got Void Stones for all the bosses but did get some level 70 currencies at the very end.

Plane of Water zone events often seem to be all Void Stones and Abyssal Crusader's Marks.