few days back just received a comment to my post at Linkedin.

"This is why an "ex" register is so important offshore. You can keep  track of installed "ex" equipment.  When it has been  replaced or repaired. Information such as class.  Gas group and most importantly the equipment serial #  and model / make type.  You can track all of the associated equipment 24/7.   This is why competent trained personnel only should be working on any "ex" equipment."

correct. no more comment from my side (+1: even onshore). VD stands for Verification Dossier (Ex register).