I've seen extension cords that are labelled #16 gauge when in fact the wires are obviously #18 (with the thin insulation).
Another day I saw a stubby extension cord (about a foot long) in a paper sleeve that proudly proclaimed "#12 gauge!"
When I took a look at the cord itself, it was embossed with #16. Very thick insulation, though. It would have passed on sight for #12.
Or was it, in fact, a #12 cord that had been mis-stamped?
This is why I make my own extension cords!