You must have finished the sanding with some very fine sandpaper. What grit number did you use for your last sanding? I would be interested to know what process you use to cut your stickers.
Seems like everybody thinks, I am a skilled puzzle builder.
I didn't use sandpaper or some kind of machine. I took a simple rasp you have to use by hand. I don't even use a bench vice to hold the puzzle. I bought the rasp two years ago and can't remember the grit number, sorry.
Processing sticker? Simple as everything else. I covered every side with appropriate colored duck tape and then cut the tape directly on the puzzle. It leaves some visible scars in the plastic when not performed carefully.