I saw a bayis that the tifera went around the whole bayis [4 sides] once, but the second time [coming back] the toifer tyed the gid a bit past halfway missing the 2 or 3 last tefiros.
I think that bdieved this was kosher, since the tefira is on all 4 sides, although not double. I didn't see anybody speak about this case.
Now I found in Zicaron Eliyahu ch. 9 that this case may be learned from the law if the tefira was torn [SA siman 33, that 2 tefiros may be permitted. I am not quoting the details]. They quote Eshel Avraham as doubting the equation, so their maskana is that if it's lacking 1 tefira, its kosher, but not 2.
I think that tefiros torn are worse then tefiros lacking.
Tzarich Iyun, maybe somebody has some information.