if you unzip the 16w39c.jar
and locate the structure folder within the assets.
open the folder for the mansion.
using a 3rd party tool (just to read the nbt data) open entrance.nbt
the 'author tag' for this, and all other structures from the mansion are Player640, Player969, etc...
what is supposed to happen is the name should be stored there, if Searge made those structures, his name would be there, if jeb_ made it, his name would be there...
You can also manually save a structure using the structure blocks, you hit save, locate the file in your saves folder. and find that the author tag is ("Player" + number) instead of your name.
In the screenshots you can see this.
The name of the player who hits the save button in the structure block should appear next to the "author" tag.