Brian Gaff (Sofa) explained :
If they were in slots and you have a gap it sounds like they were not very
well secured. If you can see the carpet edges, surely you can see the edge of
the bottom part of the strip?

What happens, is that once the carpet gets pushed and secured into the
gripper strip, the only way to remove it if the carpet needs lifting,
is to rip it off the sharp tangs of the gripper. Thus the carpet end
becomes damaged and no longer able to be effectively gripped.