A mesh read from a file can have any number of patches, and the view any zoom: a 150 x 150 mesh from a 3 MB file exported at 20x asked for about 23 million quads (2 GB), and the command's own cap of 50 rows and columns does not apply to a loaded one. One tessellation now makes at most 1,048,576 quads, the subdivision per patch giving way before that, and a mesh with more patches than that is malformed, like a point count that does not fit.