I have replaced my old Honeywell / Carrier lr1620 Thermostat with a newer Hunter 44155c unit and have a wire on the back of the old unit that connects the "Y" terminal to a terminal marked "1". Does this refer to "Y1"? Should I connect this to the "Y1" terminal on my new Thermostat?

The Wires coming out of my wall are as follows:
"G"
"RH"
"Y" (with a wire from "Y" to "1")
"W"

Should I bridge a wire from the "Y" terminal to the "Y1" terminal on my new Thermostat?

Try it because I have no idea what you started with.