THW, but research, done properly, takes a long time. A paper from 6 years ago may be perfectly respectable and recent.
When the big overviews of studies take place, they include older studies alongside more recent ones - it's not so much the age of the study, but the thoroughness of it, the size of the sample, what methodology is used and so on.
For instance, if you are looking at a connection between infant feeding and cognitive development,or heart disease, or obesity, you would need to run your study for several years, and to take in loads and loads of children (to make sure you can control for things like social background, physical health, environment). You might need to track these children for a while, right up to and even beyond secondary school - which is what some of the bug cohort studies are actually doing.
It can then take years to crunch the numbers and examine your data, and to get your paper checked by other experts ('peer review') before publication, and then it might not even be published for a year or more.
That does not invalidate your research at all. There is a lot of really good research in the medical and health field that is decades old, and which has informed later research.
Of course, sometimes old research gets superseded by new stuff, or refined, or developed - but there are no signs that the clear and consistent risks of formula are going to be shown as disappearing any time soon. This is because we know, more or less, what causes the differential in health between ff babies and bf babies, and that is the foreign protein (the cows milk) and the lack of antibodies (in formula). None of that is possible to change.