Progress Thread My First Mustang - Pace Car Mysteries

Hello out there. I am now 60 years of age, have fixed up and sold at least 20 cars in the last 25 years when I've had time, but have never owned a Mustang. 8 miles away was a 1979 Pace Car Mustang. Not been driven since 1989. Not really rotted out, paint faded like crazy to where stripes barely noticeable. Interior complete but rough. Wiring a mess, but enough where the engine turned over. Vin checked out as it's real. 302 Automatic car. I knew what one was, but never researched a Pace Car.
Here's what's baffling me.
This is an original paint car, you tell by the doors to where the two toned black at the bottom was taped off and wrapped around inside the door edges, etc. etc. When removing the interior panels, in the hatch panel on the driver side, there is a washer bottle inside the rear quarter. The filler neck obviously attaches to a hole that's between the hatch weather-strip and rear quarter in the water drain channel. Well here's the ????,
My hatch does not have the wiper arm, nor the hole cut for one or wiring for one. Also on the dash there is no switch or knob to operate a rear wiper. I don't know jack about a Mustang so I wouldn't know what the switch or knob looks like on the dash.
It's a mystery with only 2 possibility. Hatch was at some time replaced OR on the assembly line they stuffed a washer bottle in the rear quarter and then said ooops this car doesn't have a rear wiper and then still sent it on it's way. I just wanted to tell my story as I'm gonna restore this car correctly so I might have to purchase a Marti report

I have seen pictures Pace Cars having a rear wiper and air conditioning but they are very very rare, But again mine has the bottle and the hole for the filler neck but the hatch does not have the hardware for the wiper arm.

Thanks for everyone's reply as I've never owned a Mustang. Yeah the reservoir bottle looks like those in the pics. No rear wiper blade knob or switch on the dash, so I don't know what's up.