You can't do a list on it, because it doesn't appear in the the dwgs.
But, it IS there if you try the purge command and select 'View items that cannot be purged'.
If I try to bring the block back into the dwg again, it doesn't appear on the screen and doesn't even bring the defpoints layer into the dwg again. It's kinda like it just craps out and does nothing, but without any error message.