I did not see anything those links that addresses crop compaction, maybe I missed it. I did see where they were sometimes fed bread. It was interesting reading though. I don't know if your question is about crop compaction or nutritional values. You are more of a commercial type operation than a typical backyard flock. I can certainly understand you looking for a good source of inexpensive feed. Your feed bill has to be impressive.
I've seen a few warnings on here about possible crop compaction but nothing more than "bread can cause crop compaction". I certainly haven't seen why. They don't mention type of bread either. If you take certain kinds of bread and wad it up in your hand it can form a kind of lump, there might be something to it, I don't know. Their digestive juices might or might not prevent that.
I toss bread to mine all the time as part of kitchen wastes. Usually it's a pretty small amount but occasionally the wife has an entire loaf that can go. I don't throw the entire loaf to them but spread it out over two or three days. I have a relatively small flock and they will eat bread like candy. I feed stuff like that in moderation, at least most of the time.
As far as nutrition, what else are you feeding them? What kinds of bread and what is the nutritional value of everything you are feeding them including the bread? They need an overall balanced diet consisting of the nutrients they need in certain proportions. That can differ a little between layers and meat birds. Protein is important but it's a lot of other nutrients, vitamins, and minerals too. Even if I knew all that I don't have the expertise to make that assessment for you.
Maybe your county extension office can help with that. That would be my call.