Nope, they are totally independent units. But you question helped. I've tired to find any relation and succeeded. The link field was unit's "revive type". I used to copy-paste the units and forgot about this field.
Thank you. This was the cause of my duplicate command center land ability not showing up. I was at this for days and could not figure it out and would never have guessed setting "revive type" unit from command center to the copy of the command center would fix this