I have read Lenin, and yes it’s a bit more complicated since he does talk about financial imperialism but not in the same way things have developed post war. Also this is Jameson, in the introduction, describing his choice of “late.”

What ‘late’ generally conveys is… the sense that something has changed, that things are different, that we have gone through a transformation of the life world which is somehow decisive but incomparable with the older convulsions of modernization and industrialization, less perceptible and dramatic, somehow, but more permanent precisely because more thoroughgoing and all-pervasive.

And Mandel on “late”:

… will enable us to explain THE history of the capitalist mode of production and above all the THIRD phase of this mode OF production, which we shall call late capitalism’, (page 42)

Neither of these convey the idea that this is the last stage or a terminal stage, just another, most recent stage. And indeed Mandel does try and claim late capitalism is different than the imperialism described by Lenin, writing

the structure of the world economy in the first phase of late capitalism is distinguished by several important characteristics from its structure in the age of classical imperialism. (page 69)