the trouble with unwritten rules is that you may be the unlucky one who gets charged for excess baggage at check-in. my scenario is that when we go to the US on holiday we prefer to come back with 2 cases each that approach the current 32kg weight per bag ....do we risk in the future putting it in 2 bags or go for the safe option of spreading it among 3 bags each ? i would suggest it would be better all round if we went for the 2 bag policy, but that's not what the rules say.
i've had baggage problems with a certain US airline who have a glitch on their system where even written authority from their head office seems hard for the check-in agent to get their heads around.