So i took a load of screenshots to explain the issue, so will include them along the way. When looking at an item in the bottom of the shelving (3x3) that is not in a smart stack the name and tint hover above the item:
This means when trying to only select a few of the item it is hard to select the exact number (see screenshot):
This has been fixed for smart stacks (see next two images):
Hope this makes sense.