Scientists discover new human organ, a fluid-filled space called interstitium

Earlier discussion:

https://news.ycombinator.com/item?id=16689531

The following continuous blood glucose monitoring system uses interstitium fluid to measure glucose without blood.

https://www.dexcom.com/

I'm sitting here wondering, "How did centuries of autopsy miss an entire human organ?" It looks more like they found behaviour of something already known that meets the definition of an organ.