Not gonna say it ain't it, but we need more samplesI think ive said this before on here. But I think that t-haplogroup was actually eastern cushites .
It seems like too much of a coincidence after everything you mentioned on top of the fact thag the asir region the older t-haplogroup came from was a part of the tihama region where this zay'li nisba is well-known.
Although now im thinking its possible we just don't have enough t-haplogroup tested and that we'll find the older sub branches with more samples.
TMCRA dropped to 2300 ybp between Somali T-BY181210 and T-Y218135 Asir Sample, it can't just be random chance they took the Nisbah Al Zaylai by chance, maybe with the collapse, we lost older documents pertaining to lineages.