I always say I'm certain I changed 'Watchmen' less than the Coen brothers changed 'No Country for Old Men.' I'm certain of it. But you don't hear the Cormac McCarthy fans like up in arms about it. They should be. It's like an amazing Pulitzer Prize-winning book.
What guides Marxism then is a different model of society and a different conception of the function of the knowledge that can be produced by society and acquired from it.