13sex incentive

I have 2 new units I purchased for rentals and I’ve been told about the 13sex incentive if I buy 3 more I would effectively qualify. Does anyone have experience in successfully taking of advantage of this? I’ve seen conflicting information about having to buy all at the same time (which I believe is not the case) and also about it all having to be in the same town. Does anyone have experience or using this incentive currently that can shed some light?