Please help. (custom portal blocks - read description)

Hi!

I made a custom portal block that teleports me to a custom dimension. As I seen and know the block does not spawn after entering the dimension and there's no way back. So I decided to make a structure with portal spawn when I enter it. But there's a problem... If I enter this dimension more times the structure will spawn again. I was trhinking about making it spawn depending on advancements (if I made this advancement before the structure won't spawn anymore). But now it's multiplayer problem - players that haven't completed specific advancement will still cause structure to spawn. Please help me, how can I make a structure spawn only when dimension is discovered/entered for the first time. I hope I will get help from you.

Fredzik