Sorry about the vague subject line, but it's the best I could think of that wasn't a spoiler for 1917.
At the end of the movie, Schofield meets up with Tom Blake's brother (Joseph), safe and uninjured behind allied trenches near the casualty clearance centre.
But how did Joseph Blake get back from the German line? Earlier, a soldier told Schofield that Blake must have already gone over the top with his men in the first wave.
I know the attack was called off, but the first wave had already gone. Were they somehow called back? There was a three-whistle signal which seems to be the "stand down" order, but the boys attacking the enemy trenches could hardly have heard that. Would they be allowed to retreat simply because the attack wasn't going well and backup didn't seem to be arriving?