Can a white neutral wire be used as a three pole traveler wire?
The answer is yes in 1977 the white was regularly used as a switched leg. There are 2 travelers. It sounds like someone has replaced the switch in the past and mixed up a common for a traveler ( in This case common is the switch contact that toggles from 1 traveler terminal to the other) This is quite common in DIY where someone did not pay attention to the original wiring.