RainyBasil

I've been playing on a server with a few friends, we've gotten to a pretty good point in progression that we've started installing a few extra mods. There's a crafting recipe in one of these mods that has a schematic in it that can be found in ruin loot. I'm wondering if loot is pre-determined for a world seed, or rolled the moment you open a container. I don't want to end up searching for hours for something that won't happen so im hoping its rolled on opening.