He died twice!? - Multiple KIA dates (& proof!)

[Andy J2022]

Even if Jim1 is prepared to plough on through the war diary for further references to Sgt Thomas, I think it would be very worthwhile for the OP to download the diaries for himself and thus get a flavour for what the battalion were doing at the time. You can get it for free (after registering) from TNA here: https://discovery.nationalarchives.gov.uk/details/r/C7354151. You need pdf number 2 for 1917.

[jim1]

This was the Battle of Pilkem Ridge which signalled the start
of the offensive known as Passchendaele.
The 14th. were relieved on the evening of the 4th. Aug. having
been in the trenches for several days.
They were shelled almost constantly.

[hunkyhywel]

Wow thank you all this has been so helpful! I have downloaded the diary and will get through it.

-- Jim, I couldn't find that reference to him on 2nd Aug but will double check.
-- He is awarded the MM on 11th Aug but does that mean he's alive?
-- If he is still alive on and beyond 11th Aug, why are his other records unanimous that he is KIA between 31/7 and 4/8?

Thank you for your expertise and help everyone!

[jim1]

Not being recorded as deceased in the diary entry isn't particularly relevant.
The C.O. may not have been aware of his death at that time or just
chose not to include it.
All the info says he died on the 4th.

[Andy J2022]

I agree with jim1,  I think his MM was awarded posthumously, possibly related to an earlier act of bravery. The MM was gazetted on 27 September 1917 in Supplement 30312 page 10035.
Were you aware that he had previously served in the Welch Regiment as a Corporal with the regimental number 1641. If he was in the 1st or 2nd Bn Welch Regiment his number indicates that he enlisted between Jan 1886 and April 1887. However that would have made him around 49 or 50 when he died, which is possible but seems unlikely. Does this fit with other dates you may have for him? 

[jim1]

His War Gratuity shows he attested for the 2nd. time around Xmas 1915.