Facebook engineers: we have no idea where we keep all your personal data
In many ways you can think of large, long-living tech companies not unlike old cities like, say, London or Paris.  The buildings and roads you see are built on top of older buildings and ruins.  The streets are weirdly shaped and intersect at odd angles because they were made hundreds of years before and adapted over time as needs evolved.  There are catacombs underneath sidewalks and no one genuinely understands it all nor does a single reference exist that explains it.Literally everything predates everyone who lives there.  Generations and generations of original designers, architects, and laborers have arrived, plied their trade, and moved away.  There are people who are experts in certain parts, and who can build a new skyscraper at any given spot, but it is just layering and organic growth.The emergent complexity of centuries of being lived in and adapted belies easy understanding.Large tech companies are similar.  You just can't understand how "it" all works.  If you were to build it from scratch, perhaps you could, because it would be simpler and clearer, but nothing was made with the current state in mind.  It evolved and adapted over time.So reading this, I am not surprised.  I think you'd get the same answer about many other aspects of data, code, system history, etc at any other 10+ yr old tech giant.