Sadly, studies generally have the same bias. They tend to be very short, generally involve only commercially important breeds, and focus on the commercially important span of their lives.
Its why we know so many things are MINIMUM recommendations. If lesser amounts cause adverse health consequences or even "failure to thrive" in such a short time period, we can be reasonably confident that our usually longer kept, generally not "commercially-important" breeds, are likely to fare at least as poorly over their own lifespans if those minimums aren't met. Finding Maximum intakes (apart from Calcium) is even less studied.
Or, you can do as Perris and others do, provide true variety, and reasonably anticipate that your birds will (largely successfully) self-regulate intake. You can also reasonably decide that "less than perfect" is good enough for your flock. I do it myself.
