Factual error: Whilst at Sandringham estate in 1936 Bertie is waiting for the Tiger Moth plane to land. This particular plane (G-ANFM) was not built until 1941. (00:38:50 - 00:39:40)
Other mistake: When Elizabeth (and later Elizabeth and Bertie) visit Lionel's flat, they take the elevator down. With its huge windows, the flat is obviously not below ground level. And certainly no one would ascend to a higher floor only to take the elevator down to his destination.
Continuity mistake: When Elizabeth meets Lionel for the first time, her face netting disappears and reappears between shots.
Factual error: In the scene of King George V's 1934 Christmas Broadcast from Sandringham, there are factual errors. The B.B.C. Engineers are shown operating Outside Broadcast equipment in a room adjacent to the King - but the equipment (BBC Type OBA/8) didn't even come into service until 1938. It should have been type OB/7 in large mahogany cases. Also, the ornate Royal microphone cases were the wrong ones. These were the later (c1937) type first used by King Edward VIII in his Broadcast in 1936.
Deliberate mistake: The two princesses do not age, despite the film's story occurring over several years.
Continuity mistake: Near the beginning of the film, we see the Duke of York ascending a staircase inside Wembley Stadium prior to doing a speech. Visible out of a window in the stairwell is what appears to be Kingsway (later renamed Olympic Way, commonly referred to as Wembley Way), the road that leads up to Wembley stadium and the Twin towers that were attatched to the building. However, upon entering the stadium, we see the Twin towers over on the opposite side of the stadium and therefore they are on the opposite side of the stadium to Kingsway.
Factual error: In the early scene where the BBC announcer is introducing the Duke of York, the "ON AIR" sign appears to be in Helvetica font. This font was was designed in 1957, over 30 years later.
Continuity mistake: When King George finishes his "In this grave hour" speech, he puts on his coat and the coat collar is flat. When they cut back to him, his coat collar is up.
Factual error: Prime Minister Stanley Baldwin is shown resigning due to the failure of the government's appeasement policy towards Adolf Hitler. Baldwin resigned in 1937 as he chose to retire, appeasement continued under his successor, Neville Chamberlain until 1939 when war was finally declared.
Factual error: The Duchess of York's hat at Balmoral was not her fashion until the war years, (based on the Royal Air force themes).
Continuity mistake: When the Duke of York is telling his daughters the penguin story, the girls are shown from behind with each having an arm around one of their dogs, but immediately in the next scene, with the girls shown from the front, their arms are down by their sides.
Factual error: In the conversation with Bertie after delivering the Christmas proclamation, King George V refers to Joseph Vissarionovich Stalin as "Marshal Stalin". In reality, Stalin was awarded the title of "Marshal of the Soviet Union" in March 1943 after the conclusion of the Battle of Stalingrad and more than 7 years after the death of George V.
Continuity mistake: The balls on top of the red chair change directions throughout the coronation rehearsal scene.
Continuity mistake: In the scene when Bertie is meeting Baldwin to discuss David's abdication, Bertie is shown in close-up with a speck of cigarette ash on his lapel. After a cut-away the speck has gone.
Factual error: A Humber Pullman, reg no UJ7 847 is in the scene where the Duke of York enters No 10 Downing Street via the garden entrance. The scene in which it appeared was before Edward VII's abdication, but the Humber was first registered 30 Dec 1936, which is after his abdication.
Continuity mistake: In the scene at Westminster Abbey, when King George VI enters his hands are folded in front of him, but when the shot changes, his hands are at his sides.
Answer: The technique is called "masking" and all though it can sometimes help those who stutter it is not 100% reliable. It will make some stutter less, others will not notice any difference. It would probably be very inconvenient to Bertie not to hear himself at all during an important speech, not to mention that those around him might find the whole thing strange. You can read more about research on this technique and other similar ones here: http://ajslp.asha.org/cgi/content/abstract/16/1/77.
littlestar