I am intrigued by the precision to which you have quoted the uncertainty in your number of teas 13-19 implies you are certain you have at least 13 types but are equally certain you most definitely do not have 20.
Maybe the amount varies? And he just makes sure he has at least 13 choices, but 20 is excessive? Haha
I stopped counting at 19 once, but one time I did a re-count when I finished some stock and added others and it came to 13. I can't remember which came first, so I have between 13 and 19 at present. I just can't be arsed to count them again