If you look closely at this lock you will see three distinct mechanisms. The snib and two bolts.
We have seen Amaral with the assistance of a colleague demonstrating that the lock of the McCann apartment cannot be compromised using a credit card because of the impediment of a screw.
The image you have provided taken in conjunction with Amaral's documentary and the following statement, suggests to me that it would have been worthwhile to have had the lock forensically examined at the time to determine just exactly what it was capable of doing or not doing.
In the D'Ambrosio instance it appears one thing it wasn't is safeguarding the privacy of the occupants from intrusion.
WITNESS TESTIMONY OF CARLO FRANCISO D'AMBROSIO
We noticed that the cleaning personnel entered the apartment after one knock and did not give us time to respond. This was a bit bothersome and for this reason we would lock the door, and would leave the key in the inside lock.
After this precaution, the next day, the same thing happened and the cleaning woman entered even though the door was locked with the key in the lock.
We never found out how it was possible for a cleaning woman to enter after we had tried to prevent it.
http://www.mccannpjfiles.co.uk/PJ/CARLO-D_AMBROSIO.htm