After Moe says "I have a plan", he tells the others to put on armor. Larry turns to the suit of armor standing behind them to start putting it on, it then cuts to the next scene. In the next scene, the boys are all in armor; but none of it's the suit that Larry had reached for.
(at around 20 mins) When the trumpets are to play, and the boys are throwing fruit at them so they can not be played, several shots of the trumpet bells being pelted with fruit show fruit juice upon impact, and then they are clean again as the next piece of fruit hits. Also, fruit hitting the bell of a trumpet as someone is trying to play it, is going to be more effective at stopping the player from playing due to the impact against the player's mouth moreso that due to the bell being full of fruit.
After the King falls from the window and grabs Cedric, watch Larry's shirt. The new footage shows Larry's collar going from a squared off collar to triangular. Also, the King (Vernon Dent) was suffering from diabetes you can tell he is having trouble with his eyes (he would unfortunately go blind soon after).
Moe refers a wrench as a "can opener" when he makes an attempt to remove the helmet off Shemp. There was no can opener during the Middle Ages. It was invented during the 1850s. A wrench began its existence during the 15th Century. (Though to be fair, the Stooges' period films always contained anachronistic dialogue for humorous purposes.)
When the king is on the trellis and it moves away from the wall the first time, you can see the wire hidden in branches that holds the trellis to the wall.