Hello Dick:
Yes: Lonergan "consistently distinguished between theory and method." And yes, commonly, method can mean "prescriptive," as you say, or a way to do things. However, "method" in this theoretical context also refers to how our minds actually work--an analysis of the method of the mind, and not merely a good prescription for doing things.
Thus, in the theoretical context of Lonergan's work, when you say: "Lonergan's theory, in which the distinctions between experiencing, understanding, judging, deciding, and loving are expressed in descriptive and explanatory propositions," he is giving you a THEORY of the METHOD of the mind: general empirical method.
As an analysis of HOW the human mind already and actually works, we don't need to prescribe the theory in order for it to already be working in us. Thus, we can say, as you did: ". . . that you and I agree can be verified in our own personal experiences." Thus, we are not verifying that we can prescribe the method. Rather, we are verifying that, when we pay attention to our own minded operations, this happens to be what we find (and can verify).
Thus, the THEORY is of the METHOD of mind, which is also existential--we can verify it in our own personal experiences.
If you have Method in Theology, read the first few pages and chapter 1, if you have time. His meaning of METHOD is not merely prescriptive. That's a commonsense notion of method that you bring to the study--such "bringing" is not "uncommon" to those of us who try to explain what Lonergan meant by METHOD.
Regards,
Catherine