The dots and the plastic would be made of different materials meaning they have a different mass. This would mean the dots would make an effect on the weight (however small). But the engravings on the dice could cause it to be lighter on that face. Even throwing the die with a certain face up gives a higher chance of landing on the same face twice, especially if thrown by the same person.
Nothing is completely random.
the dots (pips) of die of that grade are usually the same material but just with a different color.
they have the exact same density.
the engraving though might be the only weak spot, and the way you throw them.
