My example xlights model was using a curtain like you linked to. Those curtains do not have a 4th return data wire. They either have a little circuit at the top of each drop that strips off the data needed for its 20 LEDs Or it may work like the seed pixel icicle lights work where the first LED of each drop has a fixed address.
The seed pixels with a 4th return wire are from Artacus’s Modular Matrix build