[LinuxPPS] Multiple device tree pps-gpio overlays?

[Frank Wayne]

I am trying to create two PPS devices on a Raspberry Pi 3 running Raspbian (Stretch). My config.txt contains:

dtoverlay=pps-gpio,gpiopin=17
dtoverlay=pps-gpio,gpiopin=18

This creates only a single PPS sevice: /dev/pps0. How do I get two (or more) devices?

BTW, I tried to look at archives, but the archives link (http://www.linuxpps.org/pipermail/discussions/) returns a 404.