Mine have arrived with the serial "3325".
No problems at all, guess mine have actually been in QC lol. Have been worried about this too much.
These are very well built cans. Too tight for now, but I've only laid with them for one night. Hung them on my PS so they could rest while I'm at work. :D
The hinge could be better, it keeps going back to the "default" position and tightens the head. Maybe they will open up...