yes, that creamer in your link is correct as one of the items under Registration 328744. Obviously there was some leeway in allowing related shapes to be included under a given Registered shape, and this is an example of such an instance. There's no doubt that with its art deco style handle, upper plain band with decoration of peacock and flowers, the ribbed lower half and legs, it was legitimate for the factory to include it under 328744. There may be other shapes that qualify for inclusion under this Rd. No. - I really don't know, and don't have Fred's knowledge with which to comment, although the handled squashed basket shown in Nick's most recent link was definitely one of them.
You mentioned Sowerby Rd. 328747 - although regret I've lost the plot as to exactly why - but should it be of interest I've attached a copy of the original factory drawing (now at Kew), and it too was one of the twelve Registrations from 04.11.1878. Obviously it has nothing to do with Keith's Registration.
Just a little information regarding Sowerby's introduction of these opaque wares might be of interest - details of which are taken from Raymond Slack's book....'English Pressed Glass 1830 - 1900 ............
As far as Sowerby were concerned, their invention of what they described as 'Vitro-Porcelain' first appeared in 1877, although there are pieces with lozenges showing dates from 1876.
For their Queen's Ivory ware - which George Sowerby initially described simply as 'Ivory', there were provisional patents taken out in May 1878, and Letters Patent were filed in November 1878, so it's quite possible that there weren't any pieces of 'Ivory' physically on the market until 1879 - but I'm not sure - perhaps someone can confirm. It would be interesting to know exactly which was the first Ivory Registration No.
Sowerby's first pressed glass Registrations were in February 1872 - so Keith's 1868 piece is a very rare find