I understand the logic Hugo, but I can say quite definitely that John and Lucy Hughes & family lived at the address 1 Bryn Eglwys. I know descendants of theirs and most of their children were born at that address. John Hughes himself lived to the ripe old age of 93. By a strange coincidence, one of John Hughes' descendants is currently married to one of David & Margaret Wynne's!
Back to the Census: I wonder if the explanation is that, for whatever reason, the enumerator has begun at the Bryn Eglwys end of the street and worked back to join those he had already done. The forms we are seeing are, of course, not a register he would carry around "door to door" but result of forms he will have collected or filled in for households then copied out into the return. This would explain some of the variations. If he filled in the return starting at Bryn Eglwys end and worked back, that would give 50/51/52/53 as the Bryn Eglwys houses and the remainder as Pentai. This would mean that Margaret was living at either the first or the last house of Pentai. I hope this makes some sense.