It's not great that something so basic was fitted wrong.
I'm still doing some digging as to who owned the bike post 2022 when it left Wellingborough - all the substantial itemised invoices end in 2022.
The PO I bought it from acquired the bike on 7/9/24 from someone in the Leicester area. Thats looking like 2 years of ownership where things were not fixed properly.
Looking at the dirt layers I do not think the engine has been removed since the last major engine work in late 2015, it had a top end overhual in 2019 when the cam chain was replaced.
It had a new chain & sprockets fitted in Sept 2017 by the garage though it could have been removed since then.