1638-42 Charles I Shilling - Aberystwyth S2884?

Hello all,
(Disclosure: I'm not a hammered expert!)

I found this interesting oddity which, although heavily clipped, appears to be a Charles I shilling.

According to Spink catalogue it's probably one of S2881 - S2884, but my copy (the 2018 book) only has an image of S2881 & S2884, and it doesn't quite match either:
- no plume to the left of the bust, but then again the obverse is very weak
- the XII figures are larger than either S2881 and S2884
- the reverse below the crown has a different design - it has scrolls between the centre design and the crown above
- there is no beading separating the letters from the central design on either face (S2881 has no beading, but S2882-2884 do)
- the obverse crown on the kings head looks like 2881

However, I have no other reference book to help me get a better understanding of it.
Can anyone pin it down a little closer, or advise on where to get more informaton?

Weight: 4.36g
Diameter: 26-28mm


Thanks in advance...

Photos against Spink book: