The chain stitch will naturally unravel if cut or abraded (like on our hems on jeans). On older shirts like the Ihsh-16, there was no bartack near the bottom hem. If cut, and not tied or melted, it could unravel up the seam. Nowadays there is a bartack, so if you cut the run-off at the hem, it is unlikely to unravel further up the seam. The bartack is key.