Here is how I think about it..
If you buy birds from a breeder and breed those birds together, they are the breeder's line - not yours.
If you buy birds from several different breeders, select each bird for various traits and match those birds up for different results, they are no longer the breeder's line - your line.
If you buy birds from a breeder and add it into work you've been working on for years (to incorporate a new bloodline), it is not the breeder's line either - your line.
The only way it truly remains the breeders line is if you continue to only breed that person's birds together.
Once you introduce other traits to the line, it becomes your line.
Jody