Some manufacturers are opting to forgo CDMA certification altogether and only release GSM versions of their devices. Most notably are Microsoft and HP. This is why the Lumia 550, 650, 950, 950XL and Elite x3 can be used on at&t and T-Mobile, but, not on Verizon Wireless, Sprint and US Cellular.
At some point, Verizon Wireless's traffic will migrate off of CDMA. Until then, phone specs must show CDMA, EVDO and LTE band 13 in order to access Verizon Wireless and other CDMA based networks.