Anamnesis, as it relates to forms, is a metaphor for learning but Plato uses others that do not treat objects of knowledge as something we possess already. Consider the use of myth in the following where men learn for the first time:
Socrates: It is a method quite easy to indicate, but very far from easy to employ. It is indeed the instrument through which every discovery ever made in the sphere of the arts and sciences has been brought to light. Let me describe it for your consideration.
Protarchus: Please do.
Socrates: There is a gift of the gods---so at least it seems evident to me---which they let fall from their abode, and it was through Prometheus, or one like him, that it reached mankind, together with a fire exceeding bright. The men of old, who were better than ourselves and dwelt nearer the gods, passed on this gift in the form of a saying. All things, so it ran, that are ever said to be consist of a one and a many, and have in their nature a conjunction of limit and unlimitedness. This then being the ordering of things we ought, they said, whatever it be that we are dealing with, to assume a single form and search for it, for we shall find it there contained; then, if we have laid hold of that, we must go on from one form to look for two, if the case admits of there being , otherwise for three or some other number of forms. And we must do. And we must do the same again with each of the 'ones' thus reached, until we come to see not merely that the one that we started with is a one and an unlimited many, but also just how many it is. But we are not to apply the character of unlimitedness to our plurality until we have discerned the total number of forms the thing in question has intermediate between its one and its unlimited number. It is only then, when we have done that, that we may let each one of all these intermediate forms pass away into the unlimited and cease bothering about them. There then, that is how the gods, as I told you, have committed to us the task of inquiry, of learning, and of teaching one another, but your clever modern man, while making his one----or his many, as the case may b----more quickly or more slowly than is proper, when has got his one proceeds to his unlimited number straightaway, allowing the intermediates to escape him, whereas it is the recognition of those intermediates that makes all the difference between a philosophical and a contentious discussion. — Plato, Philebus, 16c, translated by R. Hackforth
Socrates follows this immediately with an example of coming to understand music.
This method is far from the 'Theory of the Forms' Cornford (and some Neo-Platonists) connect to the picture of Anamnesis.