I am neither shocked nor surprised.
It was the 1970s. How many hundreds of times have we watched this play out on Websleuths over the years. He placed her in the Nation River exactly because it was a different province.
Communication between agencies sucked in the 1970s and we have 5 Canadian jurisdictions overlapping in this case.
Disappeared from Montreal, Quebec. Found in Casselman, Ontario. Then you've got Ottawa, Ontario (which has zero connection in this case) that is the city on the other end of the Montreal/Ottawa well travelled corridor that crosses over the Nation River.
1) SVPM - Service de police de la Ville de Montréal/City of Montreal Police
2) QPP - Sûreté du Québec/Quebec ProvincialPolice
3) OPS - Ottawa Police Services
4) OPP - Ontario Provincial Police
5) RCMP - Royal Canadian Mounted Police
Those are jsut the Canadian Police jurisdictional entities in "the Region she was found". We've also got the international border(s) with the USofA closer to Montreal than the Nation River 1.5 hours fm Montreal). It takes a mere 45 minutes to be in the USofA from Montreal.
I suspect her dental work was done in Montreal which was known (still is) for it's international flavour and availbility of services there.
From the google translate of the French CBC article:
"the family of Jewell Langford informed the Police Department of the City of Montreal (SPVM) of [her] disappearance in 1975, says Daniel Nadeau.
Despite everything, no one at the SPVM [made] a connection at the time with the discovery in May of the bound body of Jewell Langford 150 kilometers west of Montreal, near Highway 417 in Casselman, Ontario.
Similarly, OPP investigators who sought to discover the identity of this murder victim never made a connection with the disappearance of Jewell Langford which was recorded a few weeks later in Montreal."
La Police provinciale de l’Ontario (PPO) affirme que Jewell Langford a habité en avril 1975 à Montréal avec Rodney Nichols, l’homme qui est aujourd’hui accusé de son meurtre.
ici.radio-canada.ca
We don't know whether Montreal police tracked her to the apartment she shared with her killer. IMO, in those days, if an apparently respectable man told police his temporary girlfriend had left him and gone back to the US, he may well have been believed. Everyone knew about serial killers, but I wonder whether this now, all too common phenomenon of domestic murderers hiding the body, was as common as it is now. And, of course, the prejudice about a woman living with a man she wasn't married to, may have lingered.
Also, IMO, it's the jurisdiction where the body is found, that deals with it as a crime. A visitor who may have simply left, isn't classified as a crime from the police perspective, homicide division may have never been involved.
JMO