My pups are now 13 months and progressing well up to expectations. At 4 months old their drive to carry everything and anything and race around at high speed with it had me slightly concerned that I would ever get them steady. Slowly working through the sit, stop etc and keeping calm worked as it always does - well nearly always - I shall come back to that. At about 8 months that they were completely steady to the thrown dummy whether sat next to me or 20 yards away, they understood that they should not fetch it until asked to and were happy to comply.
The same with hunting, when younger they were in danger of clearing woods on their own but when I started working on quartering with them they began to understand what I wanted.
Game is important to ensure that what they have learnt is really learnt and also to work in the presence of game without boiling over and at times how to force a flush. I am now hunting them independently ( allowed to hunt together with the other dogs they will still clear woods without me only more efficiently than when younger
So I think you do need game to produce the polished hunting dog but that doesn't mean you have to have access to large amounts of it or the finest ground. Trekmoor often commented on the unusual places he found game and I had to spend much of my life doing the same, a sand and gravel pit had loads of wild partridges and I loved hunting my young dogs quietly making sure no one know I was there otherwise Heath and Safety Clad men would have removed me.
I have only had one dog I really was uncertain of steadiness with and that, in my view, was because she had so little natural drive I was always having to make sure she would to do things and make it obvious that retrieving etc was a good thing rather than having the comfort of knowing that she would do them when I told her she could and not having to worry about it. The breeder is as important if not more so than the trainer!