Yes strange part number, not vx/gm unless PSA have changed them. I looked for aftermarket replacement springs and Monroe, Sachs, KYB, LESJÖFORS etc. only appeared to list replacement front springs, so I suspect the rear springs may be unique to the J VXR, and possibly difficult to get.

Part numbers change, so can't be 100% sure, but I think the Vauxhall part number for the J VXR rear springs should be 13385461

The used part listings at,

https://www.autoteile-markt.de/shop/...6a96ec5b220bff

https://www.bildelsbasen.se/se-sv/Op...?company_id=26

also mention part number SA424432, so I suspect the ZNEOSA6085 number on your invoice, might be missing a couple of digits, SA6065??, but can't identify whose part number this is.

Whatever, if I had the rear springs on mine replaced at a vx dealer, unless I had agreed for alternative springs to be fitted, I would expect to see the correct vx part number for the replacement springs on the invoice.