Just in case anyone hasn't seen Mark's response on page 5:
"Hey everyone, I'd like to confirm either way with you the situation about serial numbers. Unfortunately we haven't been able to contact our distributor due to the holidays so I can't get any clarification. That being said, if you receive the headphones and the serial number is scratched off/missing, you can absolutely return it to us for a free refund."
- Mark, (Massdrop)
"Hey everyone, I'd like to confirm either way with you the situation about serial numbers. Unfortunately we haven't been able to contact our distributor due to the holidays so I can't get any clarification. That being said, if you receive the headphones and the serial number is scratched off/missing, you can absolutely return it to us for a free refund."
- Mark, (Massdrop)