Sid - you're quite right of course re the date of registration of the peacock's head, so not earlier than 1876.
The British publication 'English 19th-Century Press Moulded Glass' by Colin R. Lattimore lists glass patents allocated to Sowerby. Whilst most of these appear not to be relevant to the matter in question, one or two might have a connection with this post, so I will give some thought to those that look possibles, and see what comes up.
Which catalogue are you looking in re pattern 1048?