Consolidating from a different thread:
It looks interesting to me that the employee has to inform both the new pension fund and the existing vested benefits company. I wonder how Finpension still manages to not transfer one part of the vested benefits if the are notified.
As for enforcement, I read in the law:
Vorsorgeeinrichtungen und Einrichtungen, welche Freizügigkeitskonten oder ‑policen führen, melden der Zentralstelle 2. Säule jährlich bis Ende Januar alle Personen, für die im Dezember des Vorjahres ein Guthaben geführt wurde.
This would suggest to me that Zentralstelle 2. Säule has an overview of all such accounts. So it would be easy for them to check if one person has money in more than one place.