Add variable to one block

Hello in my mod I would like to add a variable to an block(golem core) if it is in the top of an earth block and keep this variable even if the earth block is broken.

I try to use block state variable but when i associate the bloc state variable to the block(golem core) on top of the earth blocke is variable affect all the blocks(all the golem core).

How i associate my variable to bust one block and not all the block?