ECN Forum Forums General Topics of the Trade General Discussion Area Circuits and GFCI - 70s code

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.