This Again depends on air line proceedures.however usualy if there are meals still left after all pax have been served,of course the seconds and the thirds may be offered if requested.
A flight attendant could also go that extra mile by offering first class and buisness class meals (according to air line proceedures) presented with minimum first/buisness equipment involved,to avoid "difference" in the cabin where pax is seated.
And the attitude of a F/A should not be,to say to the pax.."you have already eaten"...but to offer alternatives! if all mentioned above failes,you could still find fruit,cheese,crackers plentiful onboard a proper service oriented air craft/air line.