Maybe not quite gashes, but definitely substantial scuffs in the surface, hidden behind un-scuffed masking.
I had a sheet of 
plywood (medium cherry) with some noticeable scuffs/gouges on it, an inch or more long, throughout the material on one side in a few places. It was only on the actual material, not the masking, so I found out after printing! Unfortunately it was the side I printed on.
I’ve been in the habit of peeling back a corner or two to inspect for the color and general finish quality of the material (especially for walnut medium plywood for the finish…), but that won’t help finding stuff like this.
I ended up just reluctantly "whatever"ing it and used the pieces in this case, but wanted to say something so support is aware and so everyone knows to look a little more closely at things before printing. I’m not sure how I would have known about this without taking all the masking off first though.
(Sorry I didn’t get a picture before packing it up to send out.)