I came across a reel this morning by OK Crafty on FB. Wasting blanks may not be necessary as a mistake in sublimation actually is undoable!
Sublimation ink on a glass tankard that was pressed without first mirroring the design was ‘erased’ with a heat gun.
They say you need to go slowly and carefully. They advise using a dark coloured design to go over it, as there can be very faint traces left of the original. Not sure how well this would work on different substrates, but it’s a definite game-changer for mugs and glasses. 
