Their "managed recoil loads", if they indeed do, are by using less shot and/or less velocity. Since low recoil does not come from low pressure, it's not a valid reason to assume low pressures. I do believe SAAMI standards are a bit higher for the 3-1/2" magnum loads. Topics like this could be a lot easier to understand if we could get everyone to accept that recoil is not determined by the amount of pressure involved.
All of this of course stems from the oft-asked question from owners of older smokeless powder guns; "What is a "light" load?" Might as well ask, "What is the meaning of life?". It would be nice if the industry had agreed-upon standards (along with appropriate units of measurement) before they could call a shell light.
