[sawce]

The only check precache_generic/model/sound do is making sure that the native is called during plugin_precache. If that check fails, the native returns 0.

With the exception of precache_sound, the return value of the natives are whatever the half-life engine return from the API calls for the precaches (model indexes, and what not).

precache_sound always returns 1 if it passes the plugin_precache check... sounds (to my knowledge) do not use the precache index, but rather the full file string for whatever so that's not terribly useful, but it could be changed to return the value the precachesound HL-API call returns.