Yes, the NV-EC1701PLS ( 1701+) units can be joined with the older EC-1701 units. However, it is important to note that the setup is compatible only when they are in a 1-to-1 setup.
Refer to the below video tutorials to know more about joining them.
You’ll find additional resources like the Datasheet, Admin Guide, A&E spec sheet, etc on the product page here.
For more assistance,