If you’ve fled Russia and intend to lead a life of international crime, always make sure to pack an extra cigarette case, just in case you plan to accidentally leave behind your other specially-monogrammed case near one of the safes you mean to rob.
Those Russian aristocrats– they practice the prodigality!
Additional wacky bit of speculation: one of the reasons Poirot suspects the Countess, despite the fact that everyone and their aunt has the initials of B.P., is that by giving these cigarettes a careful sniff, he recognizes the smell of the contents of the empty monogrammed case. He is subsequently so taken by the smell of these exotic Russian cigarettes that he himself smokes nothing else for the rest of his fictional life. (But he cuts his cigarettes in half because Belgians, they practice the thrift.) 😉