Just extrapolating from your "night wakenings in older bubs are preventable if they have the right support and techniques".
my DD2 is almost 9mths old and might use 1-2 nappies a day and that often includes the overnight one. Just cos she is almost TT doesnt mean I can tell everyone that their babies are capable of being TT at this age if they have the "right support and techniques". In fact just cos nappy use till 2-3yrs old in AUS/UK/US is considered normal does not mean that alll babies need to be in them till then. Its dependent on baby and parent and environment.
So for your bub its abnormal for them to wake up overnight after 6mths... and for my children - its normal for them to wake overnight till 12mths ish and abnormal for them to be in a nappy after 2yrs old.