Unfortunately I don't think there's a way to get what you're after. If I'm understanding you correctly, you want to know about which devices are in scope for the PreStage enrollment, but have not actually enrolled yet, meaning not showing up in the main device inventory. I think the trouble with that is that the 64 devices in question are not in inventory yet. They are still sitting in the PreStage, and you won't be able to build any Smart Group or a search report on them since.... they aren't actually IN your inventory yet.
What you see in the PreStage section is getting pulled from ABM or ASM, as Jamf Pro ties in with those systems. Those blank device field records are not something in the main Jamf Pro inventory yet, which is why they are blank.
What I'm saying is, searches can only operate on what's in inventory already, regardless of whether the device is managed or not. Smart Groups also only work on what's already in inventory, but the difference is it only looks at managed devices, not unmanaged ones. Given this, you can't do a search or build a group on anything not already in the main inventory.
Does that make sense?
