My reasoning is once I started pulling the Holdfast armor sets out of the free track of the pass they started dropping from my umbral engrams. When I noticed this I started saving my umbrals until I could pull the free Falling Guillotine. I got it today and opened ~25 umbrals without one, obviously the loot pool is still large enough for that to happen, so I was wondering if anybody without the pass could confirm that they dropped a F.G. from Umbral Engrams.