I went back and read your post again. Today we had a drink coffee talk dogs with a threesome of about 100 plus years judging, amateur training etc going back many years. One of the topics was the dogs of old. It was on the topic of the old field trial Goldens but Labs could be included. One of the threesome is one of the top breeders in the country with field Goldens. Again this isn't a who is more correct or more knowledgeable. It was our combined concensus of the dogs of old BB (Before Holway Barty) were tough cookies but not the sharpest tacks in the box. Of course the trials of old would be hard to fathom unless you have seen a recent Senior Hunt Test. I won a Licensed Qual in 1970 with a Golden that would have most likely as I remember now, a AKC Senior Hunt Test with a triple. In those days things like dogs that were made gunshy were very common along with not stopping to the whistle, no goes, most dogs only turned one way on the cast and many were sent on back for marks and blinds. The collar as it is used today was for punishment only .Most everything was direct pressure, dog doesn't stop to the whistle you run out to the dog grab him/her put a strap on the dog tell then to sit or in very serious cases they were known to use a shotgun with small shot at about 60 to 80 yards.Shoot over the dogs head and the pellets would fall around the dog especially for not stopping to the whistle in the water.
OK lets fast forward during our "talk about dogs" session we all agreed dogs are much smarter today, breeding, just as good bitches with titles are being bred contrary to mostly titled males in the past. The advent of the "New Wave" e-collar with smart, fast ,intelligent dogs
has made training much easier and humane then in the past.
Now as an example lets use gunshyness as a problem. In the modern world of retriever training with Field Trial and Hunt Test dogs it is almost not heard of anymore. One of the major reasons is the gunfire is introduced during the retrieve, the retrieves are much longer
then years ago the shot is farther away and the dog associates it with the prey drive of the retrieve. So the correction for it is a lost art.
Years ago there was a lot more hey , hey, then throw bumpers rather then firing blank guns. More amateurs trained thier own dogs and the standard was to make loud noises when the puppies were fed, start shooting at a distance when they ate and so forth. Take your dog to a trap range etc. The shots were much closer to the dogs in training so it was not uncommon to have a gunshy dog or a thunder shy dog. The methods were many on how to correct the problem. Food motivation, staking the dog out while other dogs worked etc.
I hope the above helps somewhat in your quest and it is just one man's opinion as an explanation.