[Arran]

Another way around that lip, if you are concerned about it cutting into the insulation of the power cord, would be to add a flat fiber, rubber, or plastic washer between the knot and the lip on the inside, but I have not noticed the edge of that lip being particularly sharp. Honestly i do not know why Philco did this with their chassis, even in using the cords with the molded on strain relief, I guess that they had the expectation that someone would only buy a replacement power cord from a Philco jobber, kind of like the derangement they seemed to have against someone using metal tubes in their sets. In any even they were using these style of power cord until the early 1950s at least, all made out of natural rubber, and all now rock hard and crumbling.
Regards
Arran