I'm sure many other people who had Spanish Pointers and German Scent Hounds also didn't agree that someone might have been breeding their dog's together. But then again, you have to remember that many breeders back then didn't have the Internet and telephone either. It's a change not many of us are approving of, but we will evolve if necessary.
Take a look at all the history of many, many breeds found today. You will learn a lot, especially if you read stuff on the Dobermann Pinscher, there are many things discussed in the oldest books of documented breeding, such as white dobes, fawns and blues. Some documents even going back to the original breedings if you can find them on pedigree databases.
Yes, the GSP was by experimentation. As was the lab, the Great Dane and even Chihuahua. But there are many things you have to take into account.
The people that wanted to do these breedings had NUMEROUS breeding pairs. 10-15 of each breed sometimes, and bred them to dogs with the same physical characteristics and temperaments they wanted to get (pitbulls bred for bull fighting, pointers bred for nose and hunting, Terriers bred for their "vivacity" on rodents and willingness to kill these rodents in the cellars and pantries of castles/mansions). They would see how the dogs matured sometimes even until about 3-4 years old before breeding them.
Dogs like the Labradoodle, Puggle, etc. don't have much purpose or were bred for a purpose. Also, the thing you need to read up on is that one person was in operation of this, and kept the puppies... all of them. Typically breeds are named after the area they were born, German Shorthair, Old English Sheepdog, etc. These breeders wanted to see them mature, and out of those breedings, they bred them to another dog with the same temperament and physical attributes, etc. All this was to create a dog they wanted to see progress. Puppies in Dobes that became too aggressive or would bite their master would get put down. All the puppies, also euthanized and the parents taken out. Over in Europe, they don't tolerate aggressive dogs, here in the USA -- we are a little more lenient and put a "human emotion" on the dog, saying that it "slipped up" and give it a second chance.
You also have to remember is that if a puppy came out the wrong color (White in Dobes and German Shepherd Dogs) the litter was culled at birth and the parents fixed/put down and removed completely from the breeding program. Back then, it was the fault of the line. They sometimes even went to the extreme to the remove the siblings of the parents to prevent the dreaded color from coming back. Those dogs that managed to "squeak through" the breeding program carry the white gene now, and that's why there are some white GSDs and Dobes in existance. Same thing with the Tri-Color GSP or "Gelber Brand" in Germany. It wasn't until the dogs were in the "form the breeder wanted to see them as" that they sold the dogs. At that point it was: "I got my dog from some farmer." Pretty soon many more people saw that the GSP was quite the feather and fur dog that everyone wanted one.
These dogs were consistent - liver or white, or black and white and had the ticking and same body shape/size. They all performed the same duty equally, some better than others (or less) and when bred to one another, produced a dog that looked the same as the parents. That is when you have created a "breed" and it can no longer evolve other than small characteristics such as feeling of the coat, eye color (pale vs dark brown), long and low-set ears on the head vs high-set, etc.
Same thing with the Labradoodle, Puggle, etc. Except, there are probably thousands of Labradoodles and Puggles out there. There is no control on "creating a breed", it was just breeding a purebred to a different purebred and getting crosses/mixes/mutts. Every dog has a purpose. Non-Sporting and Toy are primarily companion dogs, but they all look relatively the same when you look and see a Dalmatian, you see a Dalmatian. Labradoodles/Goldendoodles/Puggles have a wide range of color, size, etc. Many labs are within 23-28 inches, shorthairs should be within 23-27 based on gender. Unlike a Labradoodle where they can be 20-30inches call. Too much of a range, color, or possible health issues.
Hence why Sheltie breeders have a certain height limit. Dogs too big are typically not finished with a CH or bred. It is only the bigger Shelties that typically are bred to produce herding dogs. Thus a Rough-Coated Collie, which I've heard is supposed to be the bigger cousin of the Sheltie, and was primarily used for farm work like a collie. A more laid-back of that breed, too. It's all about purpose and creating a "general standard" of what you wanted your dogs to look like, act like, perform like. You can have extremes of both in the first litter, and even the second litter. The problem you will have with your German Shorthaired Labs is that so many people are doing this breeding. There is no straight or "line" to follow. It is just people breeding their dogs together to try and get a better dog.
There is no "control group" to monitor colors, sizes, temperaments, work ethic, or even health issues. People are creating puppies for their benefit, and that's how I'm looking at it, as you can see that is where I might get a little upset.
Question -- you talk about creating a breed -- would you be willing to keep all the puppies from a litter of 12-13? What about keeping their puppies in a future litter? And the next, until you get what you want? Remember, "creating a breed" can take many generations. So hypothetically making your German Retriever or your Labrador Pointer takes 4 generations of breeding. In that time, you acquire 3 more breeding pairs. You breed several litters a year, trying to find perfection in each litter.
So, you have 4 adult, ready to breed pairs. You breed for roughly 4 years, skipping a year each breeding to watch your puppies grow until a year before trying another pair. Each pair has roughly 10 puppies born. 4(males)x4(females)x4(litters a year)x10(puppies per litter) is... 640 dogs. Would you be willing to house 640 dogs until they are 15 before you say you have the "breed you want"? Not to mention all the puppies you might need to potentially cull do to defects, the parents you might need to remove from the breedings, the future puppies that might come from generation 1 bred to generation 1 or another different parent dog on Gen0...
That's a lot of dogs, isn't it?
Then again, this is just my opinion. But read up on a lot of breeds and decide if it's worth the time and effort for one dog. You also mentioned wanting to have a good Lab that would have the tracking potential of your GSP.
What if none of the puppies came up with amazing tracking still of the GSP because you bred the GSP to a Lab with no tracking ability? Would it have been worth it to have "so-so" hunting pets?