Hello,
the following lines from online manual for Version 7.66 are not clear or implemented in a different way than expected:
Predefined primitive entities can be created with the following commands: ent_create("cube.mdl",...) creates a 16x16x16 cube model with no skin; ent_create("sphere.mdl",...) creates a sphere model with 16 quants diameter; ent_create("shadow.dds",...) creates a 128x128 transparent sprite with a dark spot in the center. Files with the same name in the path override the primitives.
If 7.66 should create the primitives even if there is no such mdl (sphere.mdl or cube.mdl) in the application path, it does not work with my version.
If it should load those mdls from template folders, it should be more clear, that this is no special new feature for ent_create. more like: There are some primitive model files prepared in the templates folder to start with.
If I am wrong, simply move this posting and your answer in a beginners area...

-- slacer