We are lucky today a comment by japatokal in This question about timatic inaccuracy and passport validity was valid. Annnnd after an hour same question is asked by a swidish user Here which I believe really helpful regarding timatic issue :)
Not sure the jpatokal Comment had much to do with TIMATIC. The 'Swedish' problem seems to be that Vietnam official visa information (EXCEPT London!) is often exceedingly out of date. As far as I am aware, TIMATIC is correct the passport needs to be valid for 6 more months.