You’re reading the term “procreative” in a far too narrow, limited way. “Procreative” does not mean that conception must result from the marital act, nor does it mean that there must be some certain chance of conception occurring. If that were the case, infertile couples, pregnant couples, and elderly couples would not be able to participate in the fullness of the marital embrace. This also raises serious questions for couples with diminished fertility: What MUST the chance of conception be for an act to be “procreative”? 50%? 20%? What about 5%? And if we use a contraceptive sponge, which is only 75% effective, well, maybe that would be OK?
Rather, “procreative” in the Catholic faith means both that the act is: (1) ordered towards procreation, and (2) that the couple is open to the blessings of life.
(1) “Ordered towards procreation” is a PHYSICAL state. It means that physical penetration is possible and has occurred without artificial physical or chemical barriers.
(2) “Open to life” is a mental state. It means that you are sincerely open to the possibility of having a child, however miraculous or remote the chance might be. Your comment that “if you have sex when you know you are infertile, you are not open to life” reveals that you have not actually practiced Natural Family Planning. Think of Sarah and Abraham: you can be COMPLETELY infertile and still be open mentally to the possibility of welcoming life and desirous or accepting God’s will. You could be COMPLETELY fertile, but unwilling to accept God’s plan for you, hoping that conception will never occur.