The cos mojave is basically just another line of mojave and if the breeder is reputable thr mojave came from a cos mojave pairing. There isn't a 'hidden gene' as much as it is just another like akin to the many lines of pastel ( lemon, citrus, etc.) what the breeder is saying is that even though your mojave doesn't look like the traditional cos mojave, it can create cos mojave babies due to the lineage that the snake is from, i.e. A cos mojave pairing