I have a Cosset-Dubrulle - on my lamp, which I think is typical, the wick adjustment and locking system are all controlled by a single knob. To open the lamp you need to turn the wick adjuster past the point where the wick is fully retracted and the flame has gone out - only then will the lamp open.
I also have a Spiralarm (one of the later brass models) and it does have a magnetic lock. It operates by placing a magnet at the base of one of the bars that surround the glass - only one of the bars is of magnetic material, the one with the lock. A shame that so many lamps have had magnetic locks disabled, I was fortunate to find one where the lock was still operational.