In my case the problem was indeed that things that were "obvious" were not documented. Some of those "obvious" things were in fact the result of decades of trai

In my case the problem was indeed that things that were "obvious" were not documented. Some of those "obvious" things were in fact the result of decades of trail and error. In the end the student did it in that particular way because it has always been done that way and for that reason found not necessary to document it. But even if you document everything many essential things will be gone. Especially knowledge about things that have been tried but don't work because failures are usually not published or documented. It is a little bit like having a document with runes of an ancient language where you may be can find out the meaning of the words and sentences. But you will never find out how the language actually sounded like.