Date uncertainty and CEF batman as train orderly?

[Mike Leishman]

Hello,

I'm uncertain of a date on James Shearer Sinclair (45461, Sapper, 3rd Field Company, Canadian Engineers)'s service record when he was attached to the 1st Brigade as a Batman (see Service Record extract). It looks like the '20th', but could also be the '30th'. In the War Diaries for the 3rd Field Company C.E. there's nothing showing any OR transfers on August 20th, but the 21st does show '1 OR proceeded on command to 1st Cdn Dvnl Train as Mail Orderly' (see dated extract). In the War Diary, 29th August, there is '1 OR transferred to 1st Bttn C.E.' but nothing on the on the 30th (see dated extract). 

So, would this indicate that James was transferred on August 20th, but wasn't recorded in the War Diary until the 21st? Or might he have been transferred on August 29th, but not recorded until the 30th? Can there sometimes be one day of 'delay' in records? 

If it is August 20th, would a 'Mail Orderly' be recorded as a 'Batman' (or might that be too loose an interpretation of the word)? 

I get more confused when I look at his pay slip, which seems to suggest he was in the 1st Canadian Engineers from September 1st (making August 30th look more like the date on his Service Record) rejoining the 3rd Canadian Engineers on September 16th (although there doesn't appear to be any rejoiners indicated in the War Diary).

Thank you in advance for any clarification/pointing me in the right direction.

Kind regards,

Mike