So, was Duralast GG? The problem with house brands is you have no idea who they're souring from or what quality they seek. The house brands can change faster than the name brands do
Wagner might be part of some private equity portfolio, which is why they have no idea what they started using afterwards. See also: Centric and Raybestos
Another possibility might be a reformulation to remove copper. Most brake pads with the sane name and part numbers are different than what was made a few years ago because of legislation regarding copper in brake pads. Ceramic and organic/NAO pads had some copper in them before.
The EBC Blackstuff I mentioned earlier never possibly contained copper, as they advertise it having zero metallic fibers.
Did you take any pics of the Duralast pads you got before installing them?