I have seen several photos from different sources of the 'pap boat' as shown in the opening post of this thread, and the descriptions seem to be equally divided as to whether the item is of glass or ceramic. There has never been an example which actually bore a registry design lozenge.
I'm pretty sure that the putative W.H. Heppell attribution is based purely on the stylistic similarity to Heppell's RDs 390584 to 390586 (photos below for permanent reference in this thread).
Also, as I'm sure most GMB members are well aware, an auctioneer's attribution (even from a supposedly reputable auction house) often needs to be taken with a substantial pinch of salt.
Fred.