Odds are, the house was originally wires with only one GFCI device, protecting the few locations that required it. The receptacle was likely placed in a laundry room or garage.
It's also likely that the device was removed and replaced with an ordinary one. Early GFCI's were rather easy to miswire, and had rather limited lifespans.
I thought about that too. However, the way the house is wired, it wouldn't be possible to get the outside and bathroom outlets on one circuit. The only outside outlet is on the same circuit as the living room outlets.
Were GFCI outlets common back in the 1970s? I really haven't see any until the early 80s.
