The Antidote Whiteback is what should be considered a variant of the Postage Paid design. Apart from the absence of any reverse side printing, hence the name, the end of the braiding around the dagger is missing. I have seen this described as missing ‘cloak’ and missing ‘vine’, but it is a sort of ceremonial braiding that features wrapped around the dagger. This can be confirmed by looking at a detailed image of the guild arms.

It is said that forty of these exist of which 10 appeared in Hogswatch covers. The other 30 appeared in Hogswatch LBEs. However these may have been issued in error, because the design was destined for the Antidote stamp.