The quality and value of certain items is calculated when that item enters the game. This includes books, paintings and artifacts among others. These values are connected to the sim who makes or finds the unauthenticated object. Skill levels, fame, career level, traits and possibly other statistics are used plus a random modifier. This means that if an item is imported via the gallery, library or the debug menu, or even if it's left in the household inventory when moving (which is an oversight I believe), all multipliers are set to 0 as there's no sim attached to the item. Only base values will apply. This is not a bug, this is how these items were designed to work in the game.
As a workaround when moving, it is important that all those items are placed in a sim's personal inventory, NOT the household inventory. This should prevent item degradation.
