What you were taught in college 15 years ago is still correct. Junk DNA does not have “a very important function”. The “subsequent discoveries” were, by and large, just a failure in science communication. Junk DNA is still non-functional, very little has changed. We know this because it’s not preserved evolutionarily. By contrast, “important” DNA is preserved from mutation (this is called “negative” or “purifying” selection) because mutating it is almost always bad for the individual. What has changed is twofold:

* We have a better handle on what constitutes noncoding, non-junk DNA. The proportion of DNA thus labelled has grown slightly (but only slightly!). We were always aware of its existence but we previously couldn’t study it easily. There are very good reasons to think that the proportion won’t grow much further. The rest is still junk DNA.

* We know more about how new genetic function can evolve using the raw genetic material in junk DNA, and how junk DNA might interfere with the proper function of cells, in particular in the presence of pathogens. But, again, the principle of this was already known (or, partially, at least strongly suspected) decades ago. It was just not studied, and we’re now able to study it better.

But our fundamental understanding of junk DNA hasn’t changed.