I think the research levels for Angels/Bob mods are slightly wrong. For example the first sorting tech gives you iron ore, copper ore, tin, lead, silicon ore but also nickel. All of those can be stacked with the basic stacking tech except for nickel. For that you need the next level. Seems kind of like a bug. There might be more such inconsistencies.

There might be, I kinda made all of this up :). I'll look into nickel when I release the 0.17 update, there seems to be some porting necessary.

If you notice any inconsistencies (in new saves, tech migration is non existent), please report them.