I'd go with Roger Payne's suggestions here. There's no obvious warning signs, and the overall condition seems pretty uniformly "experienced". Likely it was heavily used by the end of WWII and quickly moved along to a friendly nation.
In actual fact, the lack of the "S51"on the butt is a good thing! Makes me much less suspicious.
And in 1943 it's probable that it was fitted with the two position Mk.II sight, so the lack of the "S" is also good.