First off, before even starting with this, in the past sometimes schematics were changed with major unfair consequences for people already owning or producing the item, so the following mostly make sense in case of a wipe, or when creating new items: Tier changes: These are very simple, require litte thought as they can pretty much seen as bug. Some items have an inconsisten tier, if you look at the machines needed for them and the materials used. Examples -Territory units -ScreenXL