A nbt copy of a block is ABSOLUTELY the same as the first nbt copy of the original and n (+nbt) display for tooltip of (a copy of)×n a block have an "Items" block data

How to reproduce

1. Copy a command block/crafter's nbt.
2. Place the block in your main hand.
3. Change last placed command block's text.
4. Copy its nbt.
5. Place the block in your main hand.

Observed result

The placed block's text will be the text of the block copied in 1.
There are two (+nbt) in a crafter in the main hand's tooltip.