What are these uniform traces that extend to the board edge?
They are almost certainly part of a panel test fixture. Certain traces of each board on a manufacturing panel are brought out probably to a header on the outside edge where a tool is connected to perform functional testing of the boards. Once the boards have been tested they are de-panelized, but the traces remain and are never used again.
Here is an example from Dave Jones at the EEVblog:
https://youtu.be/UESc7ms4efo?t=132