Corporal Jones, of the firing squad, wears a white and purple ribbon of the Military Cross on his chest. This decoration was restricted to officer ranks. He would instead have been eligible for the Military Medal.
The piece of paper that George reads the message from after removing it from the messenger pigeon is too small to have all the words that he reads out.
Melchett says "I don't care if he's been rogering the Duke of York with a prize-winning leek!" There was no Duke of York at this time - George V had been the previous Duke before he was made king in 1910, so the title merged with the crown. Prince Albert, later King George VI, did not become Duke of York until 1920.
The firing squad's rifles are not cocked.
Blackadder mentions he will "nightly pray to the God that killed Cain and squashed Samson..." He is only half right. In the Bible it is said that Samson prayed to God to give him enough strength the pull down the temple in which he was being mocked, and Samson pulled down the temple on his abusers and himself. But God did NOT kill Cain. He branded him with a mark (hence we have the saying The Mark Of Cain) and cast him out to live as a wild beast as punishment for killing his brother Abel.