As to those who say the puppies should be taken to their new homes to be socialized in that environment from early on, I disagree. Callie didn't come home with me until she was 15 months old. Until that time she lived at the breeders, awaiting her forever home. She is the most well-socialized, out-going basenji, and she has never met a stranger. A man at the dog park recently told me he now wants a basenji because she jumped up on the bench next to him for petting & he is convinced all basenjis must be this way (despite Lola giving him the cold shoulder at the same time haha).
I have had one rescue dog (rough collie), and one dog on breeding terms (cavalier) - both came to me at the age of 14 months old.
The collie I had lived on a farm, either chained outside the house or in crate inside the hall, never been innside the house or sosialized. He was a very streetsmart dog, and had a lovley temperament. He was really great - a dog against all ods! However - it took me 6 months to rehabilitate him into being just a dog. He could not be taken on long walks in the start, his body wasn't up to it, and his head could not handle all the impressions. He was under weight, had never been loos in the house, didn't dare to do his "thing" outside of my garden, he was terrified of trains, cars, everything that moved. I gave him 3 months to prove to me that he could do better - and within 6 months he was "perfect". Something he never could have been if his genes wasn't on his side. Too bad I lost him only 4 years old due to autoimmune illness.
So of course - some dogs can handle everything - absolutly. See the same thing with a houndmix (10 months old) I got from rescue 1,5 years ago and gave to my brother - he had lived with a single mom with 3chlidren under 5 years and was sky high with stress - but he is genlte and kind as the day is long. I would liked to keep him for my self, but I was 14 days from getting Kahlo and could not work with him, and a new puppy at the same time. So I thought my brother som stress mastering training - and Truls is now doing greate! (So is my brother - who has no dog training educationg or experiense befor he got Truls. I'm just SO proud of them both.)
My cavalier, a female I got straight from the breeder at 14 months old, she was too active to just be "one of 10 dogs" and needed something more in her life to be happy, so she came to me. She had never been trained in anything exept from show, and only knew that her name was Rikke. However, she had been with the breeder everywhere and was perfeckt sozialsed. And she was the cutest dog you can imagine - even when she got sick (Syringomyelia) and was in constant pain, she never got grumpy - ever! I could do whatever I wanted with her, and she would follow me everywhere. If any breeder could give me a dog like that again, I would love to let them keep the pup after 8 weeks. But, some of her other dogs, who have had the same sozialising and "childhood" as my Rikke, was shy and nervous - why? Because not every dog is the same.
Because every dog is uniq I want to do the sosializing between 8 and 12 weeks. I need a dog that I can take with me every where - on busses, trains, at my work, on plains when I need to visit my family on the other side of the contry. So I know what I need my dogs to handle - and no - I dont think that an avrage breeder (in norway) has the chance to give 4 or more puppies everything they need in sozialising, alone, in those 4 weeks. I don't know about breeders in the UK or US, in norway breeders ofthen have a regulare job, and just breeds a litter or two a year and combines hollidays with the puppies arival so that they can stay home as much as possible with the pups to give them what they need.
And no, I don't think puppies learns to share if they live togheter more than 8 weeks, if allowed they learn that they must protect what they've got, or else some one will steal it. You snooze you loose.
I got my brussels griffon at 12 weeks, and the breeder had done a wonderfull job with her - the only thing "wrong" was seperation problems, though I don't know if that came of the age or illness (she also had syringomyelia and had to be put to sleep only 1 year old. ).