They just stopped taking the supplements, and didn't use the formula. The WIC people insisted there was nothing wrong with either. When they quit using the supplements and changed formula the problem quit.
No one did a study, partly because no one would admit there might be a problem.
So, no, you won't read the study anywhere, and there is no link to post.
I'm a great-grandfather, and between grandkids and family friends someone is always bringing a new baby by for my wife and I to coo over. Any given day, between family and friends, there is a baby on the way or just out.
It may be by virtue of different genetic groups, a different lot of formula/vitamins, or different base diets, but these people were adversely affected while the group you dealt with was not. There appear to have been no lasting ill effects.
No argument, BTW on mom's milk. They all seem to do well on that.
Some races are lactose intolerant from a very early age and Asians and many American Indians are lactose intolerant from birth, and should not drink cow's milk at all. . . and every pregnancy is different. As for formula, it is not unusual to have to try several before the infant finds one that it will tolerate well.
I don't know how long ago your anecdotal experiences were from, but most instances of such spitting up come about from ingesting too much air from bottle feeding. This problem was solved for the most part in the 1970s with the invention of the plastic baggie type "bottle" which contracted as the baby suckled the bottle and did not allow aeration of the furmulas so they did not get the gas that was so associated with burping and spitting the formula up.
What I found amazing was the number of women who had nothing but time on their hands who preferred to bottle feed their babies with VERY expensive formula instead of using what nature and God has provided in a convenient always with them means that is free and better for their babies. A week's supply of infant formula 20 years ago was $30-$40 added to a similar cost for throw away diapers. These women and girls were on fixed incomes of under $500 a month (with rent of about the same) and WIC would run out after six months of the year. No one was donating formula to the Food Banks, and you could not distribute out-dated formula. . . as soon as the sell-by date passed, even though it was still perfectly good, by Federal law it had to be destroyed.