Well then surely you will have noticed that all teenagers are individuals,and are effectively at least 2 thirds of the way to being an adult.
Blaming their parents in entirety for any behavioural flaws is as much as a cop-out as allowing any 'bad' behaviour to be dismissed as a teenage phase.
I wish you continued good luck....because yes,some of it is down to luck...in raising your teenagers to never put a foot wrong.You are obviously perfect at bringing up perfect teenagers,well done.
However,before you get too smug,I would issue a word of caution.You may wish to take into account the medical and psychological professions many,many studies...all of which acknowledge the rapid changes (hormonal,physical,psychological) that happen to each and every teenager during those brief years.You may also wish to take on board that those changes do indeed cause 'symptoms' which are usually displayed during that time of life.In the same way you could generalise the symtoms of PMT in a woman (eg sore boobs,fluid retention,snappiness,mood swings,food cravings etc etc),then you can generalise certain behaviours as being 'typical teenage behaviour'.
Although as you seem to have cracked the parenting lark,there is no need for you to be concerned.
(Lets all come back when our kids are 30,we can judge then which parents did better in the long run....the parents who refused to relinquish any control during these years...or the parents who did their best to cut their maturing kids a bit of slack and learned not to sweat the small stuff)