Breeding past F1b is where multigens come from. Usually it's F1 x F1b, but sometimes (depending on the coats) I think F1b x F1b is bred. You just don't add more poodle to F1b.
I'll have to poke my nose in here and respectfully disagree. Even though an F1b is on average 75% poodle, there will be some in every litter that are more than that (but you never know the exact percent). Even though they are "very poodley" for a doodle, they are still very much doodle, and NOT poodles. I like to think of the lab personality as a dominant trait, and even a little bit of lab goes a very long way into making a great doodle.
I don't think that we disagree....My shiloh is an F1b....and he is very poodley....but I definitely always qualify him as a doodle. Our point was more along the lines of why would you have more than 3/4 poodle...if you wanted MORE than 3/4 poodle, you might as well have a whole poodle, lol. And yes, a quarter lab can go a long way! I still want to find out for sure what Fenway is....I think I will eventually do the genetic test to find out.