[rubber_duck]

I think experience (learning where to search) is a part of it.

But a lot of the software I was working with 10 years ago was not open-source - these days I can look up the source all the way to OS level when doing Android stuff for eg.

And documentation is really just much much better - MSDN of old was considered gold standard but nowdays it would be considered bad documentation - like someone else said above docs moved from pure references to more use case focused which makes it much more searchable and eats in SO space.