1. Both The Sermons and Lectures of John Calvin in English (29 vols.) and The Sermons and Lectures of John Calvin in French and Latin (29 vols.) have 29 volumes, but down below their Product Details sections both say they've got 58 volumes. This is likely a copy/paste error from the larger collection that includes both of these two.
2. Neither of those two collections includes "This title is included as a part of the following..." in the sidebar with a link to The Sermons and Lectures of John Calvin in English, French, and Latin (58 vols.) which they are both fully contained in.
