I posted this on the K712 pro thread but it may be beneficial to put it here too.
I reached out to my contact in Vienna and got clarification. He is the product manager for the K702-65.
"Concerning the serial numbers:
Usually we do not start at zero. Depending on the product, numbers below 100, 500 or 1,000 are reserved for internal use. They are reserved for our internal pre-production test series and trial series in order to test the products, assemblies, parts, color, material finish, vibration tests, acoustic measurements, and so on. Moreover, sometimes we skip a range of numbers for customized versions. Therefore, it’s hard to tell which number will be on the last headphone leaving our factory. It might also happen that our QC department banishes some numbers in case they did not meet our strict requirements".
I hope this information will ease the minds of K702-65 owners and clear up any confusion around the serial numbers.