The magnitude distribution of objects in the Catalog is shown here, as are the distributions of the Hipparcos and Tycho catalogs over the same area of sky.  The SPM input catalog explicitly includes all Hipparcos stars but not all Tycho stars.  Still, approximately 75% of the possible Tycho stars are included as a result of the variety of sources used to compile the SPM input list, including the PPM catalog and the SIMBAD database.