Like many other folks, I found a good deal (Guitar Center) on a used Maschine MK3 and bought it, not realizing there would be registration issues. Of course when I went to add the serial # in Native Access, it was already registered to the previous owner. I submitted a support ticket to NI and within 12 hours, Julia emailed me requesting photos of my receipt and the serial# on the bottom of the MK3. I sent the photos and less than 10 minutes later, Julia responded and I successfully registered my MK3. Thank you so much, Julia - you are amazing!
For the record, I have Komplete 14 Ultimate and already had the Maschine software from the purchase of my Kontrol A49 keyboard. The used Maschine MK3 worked perfectly even when it wasn’t registered to me. Upon registering, however, I not only received some new expansions for download - I also received a couple of welcome emails with gift vouchers, so it’s worth contacting NI if you’re in a similar non-registered situation.