I don't know exactly was is happening, but the item NBT tags doesn't work any time I used them.
I've created an item that you can attach to a block, and then execute it from far away. The item should save its coordinates but when I try to execute it shows the message of non-attached that I put for these cases. I tried some other stuff with item NBT Tags and doesn't work, neither the (+NBT) thing shows up (I don't know if that should show up but doesn't show.)
Here I attach the procedures: