That's utter nonsense. Unlocked devices bought as unlocked get the update direct from Motorola.If it's factory unlocked, there's no carrier updating it. The same thing happens is it was carrier-locked but you unlocked it and changed carriers. Only the original carrier will send out updates.
Verizon sent down the October update on the XT1609, it's in-house prepaid Play variant. I just got mine today, and it was downloaded tonight. Do the unlocked XT1607s not have the October update yet?