Mishnah Berurah — משנה ברורה

And became sixteen - Meaning that all eight strings unraveled, and [the Shulchan Aruch] taught the greater [halachic] novelty (ie. that even if all 8 strings unraveled but were left with enough to tie a bow, it is still valid). But the same law applies if 2 strings unraveled and became 4 strings, it's also required to have left over enough to tie a bow, because if not then it's invalid for it's as if it is missing 2 [whole] strings from his ציצית (ie. if 2 strings unravel to less than the amount to tie a bow, -which is then as if there is no string there - then it's possible that both of those strings belonged to the same original long string that was inserted into the hole and now you are left with only 3 of the original long strings having the proper length), which makes it invalid unless he was careful at the time of tying his ציצית strings that [the same] 4 strings always stayed on the same side (ie. because then you know for sure that the 2 strings that unraveled don't belong to the same original long string, as long as they both unraveled from the same group of 4 strings). And this is as will be seen later at the beginning of Siman 12.