we are a bit late on this one - don't seem to remember it now.
In view of Kevin's earlier comments about the size of his decanter collection, I must show respect for his knowledge, but for what it's worth my thoughts are......

This very simple broad slice/panel cutting looks to me to be possibly later than the more detailed and varied cutting typical of c. 1830 - three applied neck rings were a common feature on Prussians - apparently they were the first type so treated with multiple rings to aid grip and to reinforce the neck.
Then again there were the deliberate copies from most of the major factories during the first third of the C20 - making it difficult to date these things accurately - especially from pix on the screen.
As an original shape, Prussians appear to have spanned a long period - last quarter of the C18 to well into the 1830's, but my own opinion is that this very plain cutting looks to be a long way from the fussy pre-Victorian decoration, so I'd go for c. 1840 - 70.
I wouldn't rule out the stopper as being original - although the majority of Prussians would have been fitted with a mushroom, and even rarely a target, there seems to have been some variation. When I first looked at this one it made me think it might have been moulded, but guess now we'll never know, and now too late to ask if there were matching Nos.
I wonder what it made at the boot sale.