Melchett later mistakes Baldrick's Charles Chaplin impression for an impression of Buster Keaton and remarks "The Slug Balancer seems now to be doing some feeble impression of Buster Keaton..". However Keaton would not have been widely known in 1917, as he only had small parts in Roscoe 'Fatty' Arbuckle shorts at the time. Keaton's first solo short was One Week.
Almost certainly done to set up the gags, the sequence of referenced historical events is wrong. At the beginning, Baldrick is delighted to announce that "the Russian Revolution has started", that Tsar Nicholas II is dead, and the masses "have shot all their nobs". In the final scene, General Melchett cancels the concert party because the Americans have joined the war. In actual fact, the Americans declared war on Germany in April 1917, and although this was preceded by a proto-revolution in February 1917, the Bolshevik Revolution (to which Baldrick clearly refers) was in November that year (called the October Revolution in the confused Julian Calendar), with the Tsar being murdered in August 1918.
Edmund writes a telegram to Charles Chaplin at Mack Sennett's studio, but by 1917 Chaplin had left Sennett. After Sennett, Chaplin went to Essanay & Mutual Studios (where his contract ended in 1917). In 1917 he signed a contract with First National. "Major Star" takes place in 1917 since the boys talk about the Russian Revolution and the Americans joining in the war.