Actually I find that is indistinct - and if anything makes it worse, the 'n' sound of 'teen' is not clear at all. I prefer to contrast the sounds as in '18 is not 80 and 30 is not 13' or in the sounds of the years as we speak them, 1990, 1880 ... (whoops, it is YOUR youtube - sorry sorry sorry). As I pronounce 'teen' the 'n' is quite pronounced - I don't know, maybe I exaggerate it so it sounds like tee-ne. I suggest to my students they repeat the digits separately when in conversation, to be quite sure the correct number is received.