About 25 years ago I had an ulcerated larynx with a resistant infection. I was finally referred to an ENT specialist fortunately, but for all the wrong reasons as far as the referring doc was concerned and I was kicked out of that practice when what the ENT said and prescribed contradicted 100% what she had said he would do. He prescribed 50,000 IU of fish oil A and 100 mg a day of zinc for a couple of weeks along with the antibiotic and an opioid cough syrup (to control coughing ripping the ulceration open) and she has said he absolutely doesn't do that (antibiotic and cough syrup for what clearly wasn't a strep throat) and would "show me". He stuck an optic fiber gizmo down my throat and knew in a minute exactly what the problem was. After a year of struggle and misery it was healed in 2 weeks. I currently notice a significant difference that zinc makes up to about 50mg a day. The carotenes never seemed to do nearly as much and the ENT assured me that the fish liver oil Vit A was far more active.
Generally these days I find the effects of D (5000IU) and fish liver oil A to be subtlety effective. It takes weeks to a month or more to notice any difference and then generally very subtle.
One of the ideas I suggest looking at is WHERE something breaks. Take the angular cheilitis for instance. As epithelial cell reproduction requires many vitamins, the momentary lack for some of the fastest dividing cells causes it. So an absolute lack of any of quite a few vitamins can cause it. However, in this specific reaction to "too much" B2, angular cheilitis AND dangerously low potassium (by symptoms and response) AND the accompanying IBS with a 2-3 day lag time after the cheilitis AND a worsening of CNS neurological symptoms a few days after that, I could NOT be deficient in any absolute sense of any of the vitamins. So in tottering on the edge of partial methylation block and methyltrap the symptoms appear to paradoxically shift back and forth in a way different than expected with a little more B12 causing worse b12 deficiency symptoms and even less b12 cause worse folate deficiency, because of where and how the break occurs.
Patterns of combinations of symptoms tells far more than a few symptoms not in patterns. So the classic triad pattern of symptoms that is essentially 100% right on for MeCbl/AdoCbl deficiency is 'beef red" burning tongue (epithelial, but much rarer than angular cheilitis) AND most any neuropathy symptoms AND severe abnormal fatigue. This is affecting 3 separate major system of the body. So usually the burning red tongue is typically accompanied by up to 50 or so other epithelial symptoms, and the neurological symptoms are equally widespread and the severe abnormal fatigue points at ATP partial block. A person with these 3 symptoms typically has another 100 to 200 symptoms. One non-specific symptom is nonspecific. 100 non-specific symptoms can be totally specific.
So what is the PATTERN of actual B2 deficiency that would include angular cheilitis? It most likely isn't going to include insatiable hypokalemia.. It most likely isn't going to include a worsening of Sub Acute Combined Degeneration starting within days of relatively too much b2.
These processes break at the momentarily MOST LIMITING FACTOR, and they usually break in groups of symptoms that appear to be a signature leitmotif. So certain combinations have their own leitmotif and some of them are combinations of the individual leitmotifs.
On top of that we have the leitmotifs evolving, dependent upon what other things are currently broken so they can change all the way from the bottom of the pit to finding the "last bug" as one approaches wellness.
And we, practically and scientifically, can't define what wellness looks like based on active b12s and active folate. We, individually and collectively, can't actually define how each vitamin and mineral behaves IN THE PRESENCE OF ACTIVE B12S AND FOLATE, how much is actually needed and how much might actually be too much. In the absence of active b12s and folate, B2 does NOT have the same pattern of response. I went through all that over a 30 year period over and over again, taking at least 100mg of B2 for years, and in other combinations. In the absence of active b12 and folates none of the b-vitamins made much difference. Huge amounts would sometimes force responses of sorts to take place. However, once the Deadlock Quartet are in place everything else has massively more effectiveness and what was learned with inactive or partially active cobalamins and folates has very little predictiveness of what a return to health actually looks like.
Instead research has spent the last 60 years detailing all the things that go wrong by substituting inactive or partially active cobalamins and folates and go wrong thinking they are working with the real things and repeatedly find the results "disappointing" and a "conundrum" because they don't work the way they are "supposed" to.
A recent article has revealed the obvious. The generations growing up since 1950 or so are less healthy than earlier generations. It's clear that medicine is not merely getting better at seeing these things. They can't see this at all, just all the mystery illnesses, it's 1900 all over again with Pellagra and Beriberi mysteriously rapidly increasing in the population and filling the asylums (for the poor) for those sufficiently diseased (nursing homes). Dr. Kellogg would have cured those very easily with his nutritional methods at his expensive health
Database design of medical records and so on discard most of the data needed before it is even entered into the system and are part of the cause of the problem. Asking the "wrong" questions of incorrect and incomplete data comes up with bad answers; GIGO.
This all makes understanding these things difficult.