Hmm I didn't think about that aspect.
According to the DPA though, there really shouldn't be any need for the WTS to hold ANY info on you unless you did belong to ranks of sex offenders.
According to the Spanish DPA (ARCO) you have the right to OPPOSE the data held on you and demand it be removed.
ARCO: acceso (accessing or consultating), rectificación (amending), cancelación (cancelling) oposición (opposing).
Based on that, if you demanded your ARCO rights asking them to remove all the data they had on you, then if you went to another congregation there should be no paper trail on you, just word-of-mouth (when they called to check with the elders who you are).