I should clarify my use of the word “orthodox”. Im not referring to a single set of beliefs that are “Marxist orthodoxy”, that doesn’t really exist; there are several different orthodoxies within Marxism (consider for example that there were both orthodox Stalinists and orthodox Maoists, despite those having very different ideals).

What I mean is that the Bolshevik/Menshevik split was about Lenin’s assertion that every member of their then-unified party must be fully committed the party platform in its entirety, while the Mensheviks wanted a more inclusive membership that allowed people who more generally believed in some Marxist principles and weren’t die hard career revolutionaries fully committed to every ideal of Lenin’s. “Orthodox” here just means absolute adherence to a set of ideals.