I have no facts to support my position so this post is IMO. Unless you're growing chickens off the ground on a large scale and need to get 110% out of their performance & feed costs and the difference of 1c per bird per day make a noticable impact on profits, it makes no difference in the type of chicken feed the average back yard chicken eats.
Starter, grower, finisher and layer all basically cost the same, have the same ingredients, and do the same thing, with the exception of layer & it's added calcium.
I use DuMore so I'll use their specs for discussion purposes.
It makes no difference if my hens eat 16% protein layer vs. 15% grower. They can make up the 1% difference by eating a piece of poo or a junebug.
If my hens eat 20% protein grower or 24% starter so what? I give them mooched up egg shells free choice for the needed extra calcium.
If my bittys eat 15% grower vs. 24% starter I don't care because I have no vested interest in an accelarated growth rate. I don't care if they mature in 6 months or 7 months.
Reason I feel that way is because I have bittys, growers and mature birds and don't want to handle 3 different kinds of feed. So with the exception of layer, I feed *any* chicken *whatever* kind of feed I have on hand. I never buy layer anyway.
I know this is sacriledge but I'll feed any of them scratch feed all week if that's all I have on hand.
I understand that people want what's absolute best for there pet chickens and that's cool. Your chickens, your hard earned $$$, free country, personal choice, etc but don't overthink it, except for layer, chicken feed is chicken feed.