I use the little round (or square, rectangle, etc.) pricing labels all the time for identifying the pieces for blocks, placement in rows, top, bottoms, etc.
Often it takes me weeks to get the project done and the labels have never come off nor left a residue, but still remove easily and can be reused on subsequent rows and the like.
I recently completed a postage stamp tablecloth with over 1,600 pieces and could not have kept things straight were it not for those labels. Each label got used 17 times, but were starting to lose some of their stickiness by the last row.
I think you're safe with them.