It depends what you mean by "rated"..
Normally the value specified on the power rating label is higher than actual consumption. In some cases the value is based on the fuse rating. eg It might be designed to consume 0.75A @ 230V = 172W but it might be fitted with a 1A fuse so the rating label might say 230W (eg 1A * 230V = 230W).
Something like a 50W light bulb may draw 50W when hot but it may draw more than that for a very brief period when switched on. That's because the resistance of the filament is temperature dependant, it's resistance is lower when cold.
In some/most countries regulations allow an electrician to apply a diversity rating. For example it's not unusual for an electrician to assume that a cook is unlikely to use all the rings on their electric hob/range/cooker at the same time. This may allow a big 6 ring hob to be installed on an existing circuit/wire that is apparently too small. Normally for safety reasons this circuit will be protected by an appropriate sized breaker. eg the breaker will be choosen to protect the wire feeding the hob not the rating of the hob itself. If the cook turns all the rings on at once the breaker pops. The alternative would be to rewire with a fatter wire if the supply to the house can take the increased load.