This can be so subjective.
1) When I started with one particular Cochin variety, I got the best pair I could from a Master Breeder of that particular variety. I have a closed flock - I have introduced no new blood. So now all the breeding and culling decisions are mine, but
until my birds can stand by themselves on reputation alone, I don't think I would consider ever calling them my "line". Nor would I any longer consider them "Master Breeder X Line". I would not qualify or sell them as anyone's particular line; they are just my birds, and hopefully the buyer will appreciate my breeding & culling decisions. But if someone wants to know where my original stock or bloodline came from, I have no problem with that. I never asked the Master Breeder what "lines' her birds were from - they stand by themselves on reputation alone.
2) I also participate in the Mille Fleur Cochin project - there are so many breeders involved now, the bloodlines (and genes) are all over the place. When I'm considering purchasing a new MF, I DO ask where their stock came from, as I've been following what the various breeders are adding to their projects, and I (think!) know now what will work for me and what won't. But until I can get the offspring breeding true for several generations, they won't be my "lines" either - just my version of the MF project. (There are a couple of MF breeders that have been in it from the start, have closed flocks, and you can recognize their birds - they have developed their own 'lines', and if you buy from them, you know what you're getting.)
3) I have another color variety project I'm working on by myself. In a few more generations, if I'm successful
, that WILL most definitely be my line!