In the British Army, salutes are only given, or returned, when one is wearing head-dress. Yet, on several occasions, both Sassoon and Owen salute when not wearing their caps - and they're pretty sloppy salutes at that.
Sassoon did not discard his M.C. medal as shown in this film. He tossed away the medal's corresponding ribbon. The medal itself was inherited by Sassoon's son George.
Wilfred Owen showed a draft of his poem disabled to Robert Graves not Siegfried Sassoon.
In most scenes, Sassoon is shown - correctly - wearing his Sam Browne cross-piece across his body, but in one scene it appears vertically, like one side of a pair of braces! Not only is this a major gaffe militarily, but also a lapse in Continuity.
Sassoon, and Owen, are sent to the Criaiglockhart War Hospital, a psychiatric hospital for the treatment of shell-shocked Officers (only).
However, in the film, the patients appear, in the main, to be Other Ranks, who were never sent to Craiglockhart.
Robbie Ross is shown exhorting Siegfried to attend Sitwell's Façade. The first performance was in 1922, Ross died in 1918, just before the war's end.